History of Soil Science

Vol. 66 MARCH–APRIL 2002 No. 2

HISTORY OF SOIL SCIENCE

Historical Development of Soil and Weathering Profile Concepts from Europeto the United States of America

John P. Tandarich,* Robert G. Darmody, Leon R. Follmer, and Donald L. Johnson

ABSTRACT profile concepts. This paper documents historical andgeographic aspects of the evolution of these disciplinesIn the 1870s, agricultural geologists (pioneer pedologists) in Ger-and their profile concepts from European sources tomany, Denmark, and Russia conceived of the soil profile. In more

than a century since, pedologists have generally agreed on the reasons the USA. We emphasize the interdisciplinary communi-and purpose for using symbols such as A-B-C for the designations, cation between pedologists and Quaternary geologistsbut not on the definitions themselves or the assigned significance of the that existed during and since the early 20th century, asdesignations. In this paper, we submit that two seemingly conflicting both sciences evolved their unique identities and do-classes of profile concepts evolved in the USA from European roots. mains of study. As the 21st century unfolds, we seeThe conflict stems historically from arbitrarily defined thin and thick practitioners of both disciplines attempting to reopenprofile concepts, often referred to as the soil or geologic weathering

this communication to the mutual benefit of both andprofiles, respectively. The pedologic or thin profile concept is depth-the earth sciences in general.restricted when compared with the geologic thick weathering profile.

Both disciplines developed from pioneer geologistThe geologic profile concept was developed as a homologue of theAbraham G. Werner’s geognosic concern with the sur-pedologic profile and is considered to be the full or complete profile

of weathering. Throughout the 20th century many variations of the face of the earth of the late 18th and early 19th centuriesconcept of profile appeared, and all seem to have pedo–geo conflicts, (Tandarich and Sprecher, 1994; Tandarich, 1998). Theexemplified by the myriad C horizon definitions by soil scientists. agricultural purview of the developing science of geol-Recent concepts, such as the pedoweathering profile, have integrated ogy became known as Agrikulturgeognosie, or agricul-the terminology used by pedologists and geologists into a functional tural geology (Tandarich and Sprecher, 1994; Tandarich,and useful classification for all horizons of complete profiles. Full 21st 1998). When agricultural geologist Friedrich A. Falloucentury understanding of soils beyond the historic 20th century needs

(1862) defined soil science that he called Naturwis-of agriculture, increasingly requires a knowledge of soil properties tosenschaft Bodenkunde or Pedologie, as distinct fromgreater depth than merely the historic solum and upper C horizon,Sprengel’s (1837) Bodenkunde (soil knowledge), heand makes understanding subsolum properties more critical thanstressed the need to study soil under “one main concept”ever before.(Tandarich and Sprecher, 1994; p. 7). We suggest thatthe concept for soil study, formulated as a response toFallou, was the soil profile.As pedology and Pleistocene (or Quaternary) geol-

ogy, have sprung from similar scientific roots, it isEvolution of The Soil or Pedological Profilenot surprising that they have developed homologous

The terms soil horizon and soil profile are 20th-cen-J.P. Tandarich, Hey and Associates, 53 W. Jackson Blvd., Suite 1015, tury additions to the glossary of soil science (Glinka,Chicago, IL 60604; R.G. Darmody, Dep. of Natural Resources and 1914; Marbut, 1927; Shaw, 1927). Before their inception,Environmental Sciences, Univ. of Illinois at Urbana-Champaign, 1102 scientists used other terms to describe soil, includingS. Goodwin Ave., Urbana, IL 61801; L.R. Follmer, Illinois St. Geol.

formation, soil layer or layer, vegetable mould, vegetableSurv., 615 Peabody Dr., Champaign, IL 61820; and D.L. Johnson,soil, stratum, substratum, and level. Werner, originatorDep. of Geography, Univ. of Illinois at Urbana-Champaign, 607 S.

Mathews Ave., Urbana, IL 61801. Received 5 June 2000. *Correspond-ing author ([email protected]).

Abbreviations: ASSA, American Soil Survey Association; FAO, Foodand Agriculture Organization.Published in Soil Sci. Soc. Am. J. 66:335–346 (2002).

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336 SOIL SCI. SOC. AM. J., VOL. 66, MARCH–APRIL 2002

of geognosy (modern geology) in the late 18th century, Dokuchaev (1879a, p. 25–28), in his initial lecturesof 1877 through 1878 on the Russian Chernozem pub-coined the term formation and used it to mean a discrete

rock layer or stratum observable in the field (Ospovat, lished in French, formulated a concept of soil siege (ap-pearance) as a construction (arrangement) of “trois1971; Laudan, 1987). Thus began a three-dimensional

focus on layers or strata of rocks and soils by Werner enchantillons (layers): le premier de la couche [layer orstratum] du sol [A, le second [B]– de la couche transi-and his academic successors in agricultural geology

(Tandarich and Sprecher, 1994; Tandarich, 1998). The tionaire, et le trosieme [C]– de la roche primitive [origi-nal rock].” Dokuchaev (1879a, p. 27) appears to usethree-dimensional view of a soil was called a soil section,

cut, or vertical cut. German agricultural geologists such enchantillons and couches interchangeably.In his first major work on soil published in Russian,as Fallou (1862), J.R.L. von Libernau (1868), and Albert

Orth (1873, 1875) recognized the third dimensional per- Dokuchaev (1879b, p. 70–71) used two phrases whenhe spoke of what is now known as the profile:spective of soil by the mid 19th century.“ ” (stroenie chernozem � struc-ture of the chernozem) and “ ”The Diverse European Origins of the A-B-C(zaleganiya chernozem � stratification of the cherno-Soil Profilezem). The structure or stratification of the cherno-

It has been widely assumed that Vasilli V. Dokuchaev zem consisted ideally of an individual A, B, and C(1879a, 1879b) first conceived of and published the A- “ ” (ghorizont � horizon, meaning layer orB-C profile (Tandarich et al., 1988). More accurately, stratum). The phrase Dokuchaev (1879b, p. 71) usedhe synthesized and expanded upon existing concepts. to describe the C horizon is “ ”Actually, Orth (see cover) promulgated the “boden- (korennoyu porodoyu � root rock).profil” (soil profile) as an essential basis for geognos- In the first Russian soil work published in English,tiche–agronomische Kartirung (geological–agronomic Dokuchaev and Nikolai M. Sibirtsev (1893) introducedmapping) that had been initiated in 1868 (Orth, 1873, the A-B-C scheme into the USA at the 1893 World’s1875) and, according to Muckenhausen (1997, p. 266), Columbian Exposition in Chicago, IL (Tandarich et al.,carried “the soil profile down to the parent material.” 1988; Simonson, 1989). Dokuchaev and Sibirtsev (1893,In addition, Orth (1875) developed soil groupings based p. 4) described the concept of the soil cut, in whichon profile characteristics. “always and everywhere there could be distinguished

Danish scientist Pieter E. Muller, who stated that he by the three following levels: A.–level of the soil;was influenced by Orth’s work, used the letters a, b, B.–transitive level of the soil; C.–primitive-rock (subsoil).”and c in soil profile diagrams (see cover) and analyses The thickness of the soil was represented by “A � B”(Muller, 1878). His (Muller, 1878) designations were: (Dokuchaev and Sibirtsev, 1893, p. 7). However, neithera � torf (turf), b � bleisand (bleached sand), b� � the terms profile nor horizon was used in this publi-rotherde (reddish earth), and c � untergrunde (under- cation.ground). However, the paper was not published until 9 Dokuchaev (1900, p. 35) presented a “systeme desyr later (Muller, 1887). In the meantime, Dokuchaev zones verticales de sols . . .” at the Universal Expositionhad published his concepts (Dokuchaev, 1879a, 1879b, of 1900 in Paris (Exposition Universelle de 1900 a Paris).1883) and it is, therefore, Dokuchaev’s name that has He used the term l’horizon equivalently with zone verti-become associated with the soil profile and not Orth’s cal in his publication (Dokuchaev, 1900). The A-B-Cor Muller’s. “profil de la coupe [scheme] des zones verticales des

Most soil scientists probably don’t associate Charles sols . . .” also included a D horizon when necessary (Do-Darwin with soils, but he made soil-biota process obser- kuchaev, 1900, p. 40). The D horizon was not defined—vations intermittently for over 40 yr, which culminated only described as being below a C horizon.in his “worm” book (Darwin, 1881). Russian pedologist In Russia, Dokuchaev’s profile–horizon conceptA.A. Yarilov (1936) even honored Darwin as “the evolved through application by his students, such asfounder of soil science”, adding that Rothamsted Re- Sibirtsev (1900), S.A. Zakharov (1906), and Konstantin

Glinka (1908, 1914, 1915). The Glinka (1914) profilesearch Station manager Edward J. Russell endorsed thebecame known in Germany through Glinka’s collabora-book as “the most interesting book ever written abouttion with Orth’s student Hermann Stremme (Tandarichsoil” (see also Johnson, 1999). A diagram in the bookand Sprecher, 1994), and consisted of an eluvial A, anshows a soil profile with an A-B-C-D sequence of hori-illuvial B, and the parent rock or C horizon. Althoughzons or layers, with the A indicating sod, the B the mainthe A-B-C profile was known in Europe through Mull-vegetable mould (topsoil), a C horizon representing aer’s (1887) work, it appears to have been used only instone-line, and a D apparently representing bedrockRussia (e.g., Sibirtsev, 1900; Zakharov, 1906; Glinka,(chalk).1908, 1915), and Germany (Ramann, 1911; Glinka,Dokuchaev (1879a, 1879b) credited Fallou and Orth1914) until about 1920.as having influenced his own thinking. We suggest that,

following on Fallou’s and Orth’s work, DokuchaevThe Soil Profile Concept in the United States(1879a, 1879b, 1883) crystallized the “one main” concept of Americaof the soil as an independent natural body, seen in a

profile composed of horizons that facilitated soil to be In the USA, agricultural geologist Nathaniel S. Shaler(see cover) (1890, 1891) described and illustrated dis-systematically described, compared, and classified.

TANDARICH ET AL.: HISTORY OF SOIL AND WEATHERING PROFILE CONCEPTS 337

tinct layers in forest soils: the true or upper soil (includ- teract the growing influence of C.F. Marbut.” Perhapssuch resistance by some ASSA members to either Mar-ing the forest mould), and the false or under soil (also

called the subsoil). This appears to be the first soil pro- but or the use of the profile concept led to a statementby P.E. Brown of Iowa State University made at thefile scheme promulgated by an agricultural geologist in

the USA. By the date of publication, Shaler (1890, 1891) 1923 ASSA meeting:takes precedence over Eugene W. Hilgard, who did not

What has been the accomplishment to date in soil surveypublish his profile concept until 1906 (Hilgard, 1906;research? Little beyond the accumulation of knowledge ofJenny, 1961). soil characteristics and a change of viewpoint. Both are

George Coffey (1912, p. 8) considered the soil “an most significant. Dr. Marbut in his discussion on soil classifi-independent, natural body, a bio-geological formation,” cation at the Michigan meeting of the Association (Marbut,consisting of a “surface soil” and a “subsoil.” The author 1922) emphasized the fact that a beginning has just beenof the U.S. Bureau of Soils (1914) Instructions to Field made in soil science, by the gathering of facts. He also called

attention to the changed views on the subject. It took aParties (who Simonson [1987] believes was Curtis F.long time to bring about a conviction that soil mapping wasMarbut, Coffey’s successor as head of the U.S. soil sur-not a geological operation and there are still some men invey program) defined the soil section, composed of soilthe field who see soils geologically rather than from a truematerial, as including the topsoil, subsoil, and substra-soils viewpoint.tum layers.

The suggestions which Dr. Marbut made were timelyMarbut (1927) discovered the soil profile while and should lead to a different conception of soil survey intranslating Glinka’s (1914) work during a 3-yr period relation to soil science. The study of soil profiles, the sorting(1914–1917). Marbut wrote in his personal papers that of the various factors serving to differentiate soils on theadvancement of the Russian work was a politically sensi- basis of profile characteristics and the gradual accumulationtive issue because of the anti-Russian sentiment in the of a fund of soil information, from the soil and not the

geological, agricultural, or botanical standpoint will cer-U.S. Bureau of Soils. He stated, “I had to work in secret.tainly lead to a rapid development of soil science.I was called a Russian worshipper by my own men.

It is not necessary to agree to all Dr. Marbut’s premises,Whitney had a reputation for getting rid of those whoto accept his grouping system or to follow his ideas abso-did not agree with him [e.g., Coffey]. I told him [Whit-lutely but he certainly offers suggestions which merit ourney] that I would follow his orders, but would think for careful consideration.

myself” (Lankford et al., 1985, p. 39, Folders 141–144). (Brown, 1924, p. 22)Marbut had completed and prepared a limited numberof carbon copies of the Glinka translation for circulation Brown clearly represented a faction of ASSA mem-to a few selected persons by 1920 (Lankford et al., 1985, bers willing to evaluate and accept new ideas regardless

of origin. His statement reflects an emphasis on thevol. 5, p. 40). However, it appears that he waited touse of the profile as a concept for studying soils ashave the translation published until the U.S. Bureau ofindependent entities, paving the way for the develop-Soils head Whitney was too ill to oppose it. The trans-ment in the USA of what is now known as pedology.lation was finally “published” (albeit in mimeograph

Bridges (1997, p. 52) relates a personal communica-form) in conjunction with the First International Con-tion from Simonson who stated that during 1924 “agress of Soil Science in 1927 (Marbut, 1927).circular was issued which contained instruction on theuse of the A-B-C designations; its anonymous authorUnited States’ Soil Profile Evolutionwas Marbut.” This explains how a symposium “Profilein the 1920s and 1930sStudies of Four Major Soil Groups” could be organized

Marbut introduced the soil profile concept without at the 1924 ASSA meeting in Chicago. The presentedusing horizon designations at the American Association papers, published later, used the A-B-C designations inof Soil Survey Workers meeting in East Lansing, MI in a generally consistent way: J.C. Russell and E.G. Engle1921 (Marbut, 1922). Merris M. McCool and Jethro O. (1925) on the central prairies, H.H. Krusekopf (1925)Veatch, also without horizon designations, did the first on brown soils of the north central states, Earl Fowlerprofile-oriented work in the USA, in Michigan in 1922. (1925) on coastal plain soils, and Veatch (1925) onThey presented their work at the American Soil Survey northern podsol soils. Charles F. Shaw (1925; see cover)Association (ASSA) meeting held in Urbana, IL in 1922 also used the A-B-C designation in his report on Austra-(McCool and Veatch, 1923). Marbut touted the work lian soils. Veatch (1925, p. 27) refers to the A-B-C profileas the first “work of the kind to be done in the United as “the Glinka scheme.” This was 2 yr before the mimeo-States” (McCool and Veatch, 1923, p. 165). At the 1922 graphed Marbut (1927) translation of Glinka was avail-meeting, it was recommended, “that the Association able in the USA; carbon copies of the translation wereencourage the more intensive work in the individual circulating within the professional community.states regarding ‘Characteristics of Soil Profile’” A symposium on “Soil Profile Studies” was held at(O’Neal, 1923, p. 173). The first person to publish the the 1925 ASSA meeting. All of the presentations andA-B-C designation system in the USA was Raymond subsequent publications featured the A-B-C system:S. Smith of Illinois, in a paper given at the 1923 ASSA Thomas D. Rice (1926) on prairie soils, Mark Baldwinmeeting in Chicago (Smith, 1924). (1926) on northern timbered soils, William Hearn (1926)

Simonson (1987, p. 13) has declared, without docu- on southern soils, and Macy H. Lapham (1926) on west-ern soils.mentary evidence, that the ASSA was formed “to coun-


Table 1. Correspondences of soil horizon and layer concepts as National and International Profile Formalizationgiven in Shaw (1927).

When Charles E. Kellogg (see cover) became theSoil horizon Soil layer

Chief of the Soil Survey after the death of Marbut inA (A1 ) eluvial horizon Surface soil 1935, he defined the A and B horizons (the solum) forA2 Subsurface

use in the national soil survey (Kellogg, 1936, 1937).B–illuvial horizon SubsoilC–unweathered parent material Substratum While the emphasis on the A and B horizons has re-

mained unchallenged to the present, the C horizon’sdefinition and application could be called inconsistent.

In 1926 Shaw, who was serving as chairman of the Kellogg (1930, p. 35) initially described the C horizonASSA Committee on Terminology, proposed a termi- as “parent material that has been unaltered by soil-nology glossary (Shaw, 1927). Here, for the first time, building forces.” He (Kellogg, 1936) then called the Cdefinitions were compiled, including soil layer, soil hori- horizon “weathered parent material.” Later, he and thezon, and soil profile. The term soil layer was used in Soil Survey Staff characterized the C as “little altereddescriptions of the soil section since the inception of by pedological processes” (Soil Survey Staff, 1951,soils surveys in the U.S. Bureau of Soils in the late 1890s 1962). This ambiguous C concept became dogma.(U.S. Bureau of Soils, 1914; Simonson, 1987). The terms This dogmatic C horizon became part of the theoreti-horizon and profile were more recent arrivals through cal base of pedology through Roy W. Simonson’s work.Glinka (1914) and Marbut (1927). Shaw merely equated He (Simonson, 1959, p. 152) proposed that it had anthe definitions of soil horizon and soil layer; the corre- “indefinite lower boundary.” According to Simonsonspondences between them are summarized in Table 1. and David R. Gardner (1960, p. 128), the pedon concept

The horizon–layer synonymy was used for educational “would . . . [extend] downward far enough to includepurposes: horizon was used in scientific contexts and the full set of genetic horizons. The lower boundary [oflayer in school or lay contexts (Lapham and Marbut, the C horizon] cannot be defined clearly, nor can it1931). Currently, layer is used by geologists and sedi- be established conclusively in many instances by directmentologists to refer to “any tabular body of rock, of observation. It must remain somewhat vague, as doesice, or of unconsolidated material, lying in a position the lower boundary of the soil itself.”essentially parallel to the surface or surfaces on or On an international level, the Food and Agriculturalagainst which it was formed, and more or less distinctly Organization (FAO) (1977, p. 18) stated in its horizonlimited above and below” (Bates and Jackson, 1987, p. designation guidelines that the “C . . . should not be la-373). The term layer has been broadened in a soils sense beled as [a] ‘soil horizon’ but as [a] ‘layer,’ since [its]to include horizon. Horizon, although originally defined characteristics are not produced by soil forming factors.”as a layer in a soil profile, has come to mean a layer or However, the FAO also declared that the C horizonmaterial altered by pedogenesis (Soil Science Society “does not show properties of any other master horizons”of America, 1997). A soil profile was defined by Shaw (FAO, 1977, p. 20).(1927, p. 68) as a “vertical section of soil from the surface We have listed subsolum horizons and their defini-into the underlying unweathered material.” tions in Table 2. In most instances the designations were

Shaw presented the glossary at the First International assigned to intervals between the solum and unweath-Congress of Soil Science in 1927 (Shaw, 1928a), and ered material or bedrock.again later that year at the 1927 ASSA meeting whereit was formally adopted by the society (Shaw, 1928b). A-B-C Profile Expansion And AlternativesThe Shaw (1929) profile shows an appreciation for char-acterizing the region beneath the A and B horizons: C1 Efforts have been made to expand existing or develop

alternative horizon designation systems. D.W. Pittmanrepresents oxidized, leached, C2 is oxidized, unleached,and CN equals unaltered parent material (the CN desig- (1932) promulgated the descriptive system proposed by

A.N. Sokolovsky (1931, 1932). In this scheme, a P (par-nation, rewritten as Cn, was used 45 yr later by Birke-land (1974) for unaltered parent material). ent rock) horizon was used rather than C. In addition,

the unaltered parent material was designated with aAfter the horizon definitions were adopted by theASSA in 1928, no real consensus was reached in the notation z following the P (Pittman, 1932).

Eugene P. Whiteside (1959) proposed a series of mor-profession regarding horizon definitions. The ASSA ap-pointed a Committee on Horizon Criteria, chaired by phogenetic horizon designations in place of the A, B,

and C. His profile below the solum consisted of pedoge-E.A. Norton, to develop standard horizon definitions.C.C. Nikiforoff (1931) cursorily reviewed the history of netic horizons W (water leached, oxidized, and slightly

altered) and X (unknown). These pedogenetic horizonsthe A, B, and C horizons, possibly as background forthe committee. The committee met from 1931 to 1934 were distinguished from petrogenetic horizons P (pri-

mary material—unaltered, unleached, and unoxidizedand the results were reported by Norton (1932, 1933,1934, 1935), but no consensus on standard definitions layer) or U (underlying, unrelated materials). In addi-

tion, Whiteside (1959) advanced a total profile concept,was reached. In its final statement, the committee de-cided to leave horizon concepts flexible and their defini- the soil, which extended from the surface (V) to the

unaltered (P). While Whiteside’s proposals were nottions deliberately imprecise to allow application over awide variety of conditions (Norton, 1935). wholly adopted, his E horizon designation was used in


Table 2. Summary of subsolum horizon and layer concepts.

Horizon or layer

Placement (subsolumSymbol or unless otherwisedesignation indicated) Definition or description Reference

C Subsoil Subsoil, parent material or rock Dokuchaev (1879, 1883, 1900), Dokuchaev and Sibirtsev (1893)‘‘Feebly altered’’ parent material Zakharov (1906) in Zakharov (1927)

Substratum Unweathered parent material Shaw (1927, 1928a, 1928b)Unconsolidated material little affected by Kellogg (1930, 1936, 1937), Soil Survey Staff (1951, 1960, 1962,

pedogenic processes and lacking prop- 1975, 1981, 1993), FAO (1973, 1977)erties of O, A (including A2 later renamedE), B, and R; (includes C1, C2, D, G)

Oxidized or gleyed, unleached Follmer et al. (1985), Tandarich et al. (1994)C1 Weathered, leached parent material Marbut (1924)

Altered, unleached parent material Fowler (1925)Basal horizon of weathering Veatch (1925)Decomposed, disintegrated, oxidized, leached Norton and Smith (1928), Shaw (1929)Slightly weathered Kellogg (1930, 1936, 1937), Soil Survey Staff (1951)

C1 Transitional to C2 (viz.) Leached, oxidized Follmer (1979)C2 Decomposed, oxidized, unleached parent or Marbut (1924), Shaw (1929)

sourceUnaltered, unleached parent material Fowler (1925)

Below substratum Below substratum: unaltered geologic Veatch (1925)formation

Decomposed, lesser disintegration, oxidized, Norton and Smith (1928)leached

C2 Oxidized, unleached Follmer (1979)C3 Decomposed, slight disintegration, oxidized, Norton and Smith (1928)

leachedC3 Transitional to C4 (viz.) Elements of C2 and C4 horizons present Follmer (1979)C4 Unoxidized, unleached (unaltered) Follmer (1979)CC Oxidized, unleached Frye et al. (1960, 1962), Willman et al. (1963, 1966)Cn, Cn Unaltered parent material Shaw (1929), Birkeland (1974)Cox Oxidized, unleached Birkeland (1974)Cr Strong reduction from groundwater influence FAO (1973, 1974, 1977)

Weathered, partly consolidated or soft Soil Survey Staff (1981, 1993)bedrock

Cu Unaltered parent material Birkeland (1984)Below C Dokuchaev (1900)

Ochre gley Zakharov (1906) in Zakharov (1927)D Slight decomposition, oxidized, calcareous Norton and Smith (1928)

Stratum unlike C and/or solum Kellogg (1930, 1936, 1937), Soil Survey Staff (1951)Below C Unaltered, unoxidized, unleached, Follmer et al. (1985), Tandarich et al. (1994)

unconsolidatedDr Below C Consolidated rock like that from which C (or Soil Survey Staff (1951)

solum, if no C is present) has developedE Unaltered parent material Norton and Smith (1928)G Reduced gley or glei Zakharov (1906) in Zakharov (1927)

Glei (groundwater influenced) Glinka (1914)Within the C or beneath Altered gleyed parent material Kellogg (1930, 1936, 1937), Soil Survey Staff (1951)

Undifferentiated, unripe material Brinkman and Pons (1973), Dent (1986, 1993)M Irreversibly indurated (non-pedogenic) Soil Survey Staff (1951)OU Oxidized, unleached Hallberg et al. (1978)P Parent rock Pittman (1932)

Unaltered, unleached, unoxidized Whiteside (1959)R Hard (consolidated or indurated) bedrock Soil Survey Staff (1962, 1975, 1981, 1993); FAO (1973, 1974,

1977)S Sedentary weathered zone Nye (1954)U Underlying material unlike overlying material Whiteside (1959)UU Unoxidized, unleached Hallberg et al. (1978)Unaltered Unoxidized, unleached Frye et al. (1960, 1962); Willman et al. (1963, 1966)W Weathered zone Watson (1961)Zone 4 Oxidized, unleached Leighton and MacClintock (1930, 1962)Zone 5 Unoxidized, unleached Leighton and MacClintock (1930, 1962)

Below oxidized, Oxidized, unleached Kay and Pearce (1920), Kay and Apfel (1928), Kay and Grahamleached (1942)

Below oxidized, Unoxidized, unleached Kay and Pearce (1920), Kay and Apfel (1928), Kay and Grahamunleached (1942)


the FAO (1973, 1977) and later Soil Survey Staff (1981, [A�B horizons] itself is a deep zone of material whichcannot be classed either as rock or as soil.” He called1993) systems.

E.A. Fitzpatrick (1967, 1980, 1988) also broke with this zone the C horizon and defined it as “the place ofdecomposed rock material which is gradually changingtradition and formulated an alternative approach to the

A-B-C-horizon designation. His system categorized all into soil” (Jurney, 1935, p. 57). O.C. Bryan (1935, p.66–67) used the designation C for disintegrated andmajor horizons into 77 types based on their own charac-

teristics and diagnostic properties. Such a large system decomposed rock in the soil profile.In the tropics, as one of us pointed out (Johnson,adds precision and important distinction, but is difficult

to remember and apply in the field. 1994), an alternative profile scheme was formulated bysome workers in the 1950s through 1960s. In his cocoaThe study and classification systems of soils around

the world were largely developed independently from soils studies, C.F. Charter (1949) observed that humidtropical soils in South America and Africa typically ex-one region to another. The systems were largely built

on regional experiences. Nevertheless, in recent decades hibit three-layered profiles: a fine fraction mantle (top-soil, surface mantle), above a stony layer (stone-line),the A-B-C concept of soil profile has been used to de-

note the master horizons of most soils of the world. over weathered regolith or weathered bedrock. P.H.Nye (1954), working in Nigeria, subsequently gave twoThe A-B-C notation is most easily applied in youthful

landscapes, particularly in those regions glaciated during master horizon designations for such three-layered soils:a surficial Creep (Cr) Horizon that includes the surfacethe Pleistocene. Its application in areas outside of glaci-

ated regions has been more problematic. mantle and the stone-line), and a Sedentary (S) Horizonfor the subjacent weathered zone. J.P. Watson (1961),working in southern Africa, renamed the three horizonsA-B-C Use in Deeply Weathered Profilesas follows: M for mineral mantle, S for stony layer

In many nonglaciated areas of the world, deep weath- (stone-line), and W for the weathered zone, a muchered profiles have developed. The application of the C simpler and more straightforward scheme. Donald L.in these areas was as uncertain as the designation of the Johnson (1994), in comparing humid tropical soils withmaterial that had weathered from the bedrock. G.F. humid midlatitude soils, averred that the midlatitudeBecker (1895, p. 289), in his studies of the southern A-E-B-C scheme is basically the same as the M-S-WAppalachian gold fields, noted that geologists had used scheme, where A � M, E � S, and B � C � W, andthe German words “geest” (meaning dry land) and that the same basic genetic processes produce them“gruss” (meaning transported angular material; it now (many midlatitude soils have stone-lines at either themeans an in situ weathering product) when describing AB horizon interface, or the EB horizon interface).decomposed bedrock. Considering these word uses un- The deeply weathered profiles developed in bedrocksatisfactory, he proposed the term “saprolite [from the began to receive more attention from pedologists sinceGreek ��, meaning rotten] for thoroughly decom- the 1950s (Stolt and Baker, 1994). The term saprolite,posed, earthy, but untransported rock. When the exact as originally defined by Becker (1895), began to be usedcharacter of the original rock is known it is easy to in U.S. soil surveys in the 1960s. Larry T. West (personalqualify this term and to speak of ‘granitic saprolite,’ and communication, 2000) stated that the earliest use ofthe like” (Becker, 1895, p. 289–290). Although Becker the term that he had seen was the Clarke and Oconee(1895, p. 290) observed soils above the saprolite, he Counties, Georgia soil survey correlated in 1965 andneither described the soil and saprolite nor attempted published in 1968 (Robertson, 1968); and that the termto genetically relate them in a profile. appears to have entered the published soil science litera-

Fowler (1925) was the first to apply the A-B-C profile ture (at least in the USA) by 1973 (Ojanuga, 1973).to deeply weathered soils of the Piedmont and Coastal H.H. Eswaran and W.C. Bin (1978) recognized dis-Plain. He subdivided the C horizon into two members: tinct zones within the weathered bedrock portion ofthe C1 was parent material weathered from bedrock profiles and modified the concept of G. Stoops (1967)that retained its geological character and could extend to address the situation. Their zones are briefly de-downward many feet, and the C2 was the unaltered scribed as: � A � B, � � accumulated gravel eitherparent material bedrock (Fowler, 1925). Marbut (1928), with (�1) or without (�2) petroplinthite, �m � mottledin his USDA Graduate School lectures, recognized that zone with plinthite, �p � pallid zone, � � evident rockthe C horizon of certain soils in the Piedmont often structure, and R � cohesive rock (Eswaran and Bin,

1978).extended down several tens of feet (several meters) intothe disintegrated and decomposed (his terms) rock. He Stanley W. Buol, his colleagues and students, have

studied profiles in deeply weathered rock worldwidediscussed analyses of C horizon samples at 25 (7.6 m)and 75 foot (22.7 m) depths (Marbut, 1928). Shaw (1929) for over 25 yr. C.S. Calvert et al. (1980) applied the

designation R-S to the saprolite and the R-U to theincluded disintegrated bedrock in his C horizon defini-tion. William Battle Cobb (1931, p. 87) in his study unweathered bedrock portion of these profiles. Within

a short time, E.L. O’Brien and Buol (1984) used C forof chemical constituents lost from horizons in selectedGeorgia soil profiles, distinguished between the C hori- saprolite. After further consideration, T.J. Rice, Jr. et

al. (1985), R.A. Rebertus and Buol (1985), and Griffinzon and the “less weathered lower horizons” that hecalled “weathered rock.” R.C. Jurney (1935, p. 57) rec- and Buol (1988) applied Cr to the saprolite portion of

the profile. The designation Cr was originally used inognized that “lying between the bedrock and the soil


the FAO (1973, 1974, 1977) system for strong reduction Leverett and Alexander Winchell, were also active re-searchers in what became known as Pleistocene orfrom groundwater influence. However, the Soil Survey

Staff (1981, 1993) chose to designate weathered or soft Quaternary geology (Tandarich, 1998). The interest insoils among Quaternary geologists has expanded to in-bedrock by Cr.

However, Buol found imprecision in the concept of clude the subdisciplines of paleopedology and soil stra-tigraphy.saprolite, its use and application and has developed a

provisional taxonomic classification for it (Buol, 1994). In the 20th century study of Pleistocene geology, theconcepts of the geologic weathering profile (TandarichMost recently, P.J. Schoenberger et al. (1995), Li et al.

(1997), and Buol et al. (2000) have used the C for sap- et al., 1988), and soil stratigraphy (Morrison, 1967, 1978)evolved to form a geological basis for understandingrolite.soils. Initially this evolution took place in schools andgovernmental agencies within the mid-continental USAThe Solum: A European Scientific Soil Conceptwhere glaciated landscapes were prevalent. These insti-

The struggle with soil horizon and profile concepts tutions included the Universities of Chicago, Illinois,was not unique to the USA. In Finland, Benjamin Frost- and Iowa, and the geological surveys of midwesternerus recognized that there was no one language in the states.northern European and Scandinavian countries that had Colleagues of Shaler and Hilgard, Chamberlin, anda scientific word for soil. His prime example was the Rollin Salisbury at the University of Chicago, trainedwidely used German word boden, meaning soil, topsoil, George F. Kay (see cover). Kay was the originator ofor ground, in this linguistic category. Consequently, the term gumbotil (Kay, 1916) and geologic weatheringFrosterus (1924) proposed the term solumhorizont (a profile (Kay and Pearce, 1920) concepts. Kay (1916, p.singular German noun, from solum—the Latin word for 637) characterized gumbo(til) as “a grayish, tenacious,soil) for that portion of the earth surface affected by thoroughly leached, and nonlaminated joint clay.” Ac-soil-forming processes. Frosterus (1924) recognized that cording to Kay (1916, p. 637), “gumbotil is chiefly thethe Solumhorizont extended from the surface down- result of weathering of till,” but he never referred to itward and included (i) a surface zone of depletion, (ii) as soil. He gave a paper before the ASSA in 1929 (aa zone of enrichment and (iii) a zone unaffected by soil- reworking of portions of Kay and Apfel, 1928) entitledcreation processes (the Untergrund). The solumhori- Gumbotil, its characteristics, origin and significancezont concept was advanced at the 1924 International (Kay, 1930). Kay described stages of the alteration pro-Conference on Agrogeology in Rome (at which the cesses of the gumbotil and weathering profile:International Society of Soil Science was formed) that

solution, hydrolysis, the formation of colloids and crystal-was attended by a few U.S. scientists, including Marbut.loids, precipitation and leaching, the gradual passage down-The concept name was shortened to solum whenward of all the transportable elements of the till, includingbrought back to the USA.the iron, the silica, the colloidal clays, and similar colloidalIn 1926, Shaw (1927) defined the solum as the weath-silicates. The resultant residuum of the chemical leachingered part of the soil profile, and had restricted the term process is a practically insoluble stratum—the gumbotil. In

to the A and B horizons. Marbut (1928, 1951) called addition, such physical factors as wind action, freezing andthe solum the “true soil,” the “mature soil,” or the “soil thawing, and burrowing of ground animals may have playedlayer.” However, outside of the USA, some scientists, some part (Kay and Apfel, 1928, p. 111–112; Kay, 1930,such as D. Baize (1993) in France, appear to retain p. 134–135).Frosterus’ original concept of the solum as the weath-

However, Kay stopped short of declaring the pro-ered portion of the earth’s crust; his conceptual solumcesses listed above to be soil-forming processes and theand reference profiles include the A, B, and C horizons.weathering profile, including the gumbotil, to be co-The original solum concept embodied the entire soilequal to a soil profile. Yet he (Kay and Graham, 1942)profile, not just the A � B. However, the solum conceptequates the gumbotil and weathering profile zones asin the USA has been restricted to the A and B horizonsdefined by Morris M. Leighton and Paul MacClintockfor the last 70 yr and this notion has spread globally.(1930; see below) to “soil profile horizons.” Kay’s weath-Nevertheless, a concept of a total solum incorporatingering profile zones are unnumbered or otherwise sym-the entire A-B-C profile has utility and is suggested inbolically designated: gumbotil, oxidized and leached till,the profile concept of Norton and Smith (1928), the soeloxidized and unleached till, and unoxidized and un-concept of Whiteside (1959), and the pedoweatheringleached till (Kay and Apfel, 1928; Kay and Graham,profile of John P. Tandarich et al. (1994).1942).

We suspect that Kay was influenced by the work ofDevelopment of Homologous Profile Concepts Stevenson and J.F. Barker (1911) at Iowa State Univer-sity on “gumbo soils” of Iowa. As Kay’s archival papersThe subdiscipline of geology called Pleistocene geol-

ogy or Quaternary geology arose from the Wernerian on the weathering profile are missing and presumedlost, we may never know if he corresponded with soilgeognosic roots from the late 18th through the 19th

centuries, as did agricultural geology. Many of the pio- scientists as he formulated his ideas. Kay collected publi-cations on soils, particularly soil survey reports, andneer geologists who practiced agricultural geology,

such as Amos Worthen, George H. Cook, Dokuchaev, corresponded with soil scientists Bushnell, Conrey, Nor-ton, Rice and Smith in the 1920s and 1930s (Kay, n.d.).Thomas C. Chamberlin, Hilgard, W.J. McGee, Frank


A student and colleague of Kay, Leighton (see cover), through 5 were within the C horizon: Horizon 3 wasoxidized and leached; Horizon 4 oxidized and un-refined the weathering profile concept. Leighton (1958)

relates that, during his early years at the University of leached; and Horizon 5 unoxidized and unleached (un-weathered). The Leighton and MacClintock weatheringIllinois, he was inspired both by Glinka’s work (1914)

and Marbut’s. Between January and July of 1923, Mar- profile was used in Illinois and elsewhere in Pleistocenegeologic studies until a revision was made by John C.but gave a series of lectures at the University of Illinois

that Leighton attended, and field trips were organized Frye, H.B. Willman, and Herbert D. Glass. This revisionbegan to evolve in the late 1940s and the 1950s.by university faculty members (Smith and others) to

allow Marbut to view Illinois soils and comment on their Frye, a Pleistocene geologist at the Kansas GeologicalSurvey between 1942 and 1954, became acquainted withcharacteristics and classification. The note cards of the

soil profiles Marbut saw on this field trip are in the pedologist James Thorp, the U.S. Bureau of Chemistryand Soils, Division of Soil Survey regional correlatorMarbut Collection (Lankford et al., 1985).

As a result of this experience Leighton (1958, 1959; for the Great Plains. Glass (personal communication)stated that Frye became sensitive to the soil scienceLeighton and MacClintock, 1930, 1962) credited Marbut

for insights obtained on the soil profile and its applica- literature and soil studies relative to Pleistocene stratig-raphy through communication with Thorp and his pub-tion to studies of Pleistocene weathering profiles. In

addition, Leighton had good rapport with the soils fac- lished works (e.g., Thorp, 1949; Thorp et al., 1951).Frye came to the Illinois Geological Survey and suc-ulty at the University of Illinois during the 1920’s. He

particularly credited Smith and Norton, who were work- ceeded Leighton as Chief in 1954, holding the post until1974. Willman, a stratigrapher, had been working at theing on their own profile concepts at the time (see above

and Table 2), for their “active collaboration” who “di- Illinois Survey since 1926, and Glass, a clay mineralogist,since 1948. The three began collaborating on Pleistocenerected attention especially, and with great helpfulness,

to the detailed characteristics of the soil and immediate soil studies in 1958 (Glass, personal communication,subsoil materials” (Leighton and MacClintock, 1930, 1987) and produced major works on the concepts ofp. 30). gumbotil, accretion-gley, and the geologic weathering

Leighton (1958, p. 704) explained that the weathering profile concept (Frye et al., 1960; Willman et al., 1963,profile “was used as the geologic homologue of the 1966).pedologic term soil profile and also in recognition of Close linkage with the pedological profile is an inte-the differences in the objectives, scope, and application gral part of the Frye, Willman, and Glass profile thoughof geology and pedology.” Leighton (1958, p. 705) em- they were uncomfortable with the term horizon, prefer-phasized that “it should be clear that the geologic terms ring instead zone. Their A-zone and B-zone are equiva-weathered zone and profile of weathering and the pedo- lent to the A and B horizons of the 1951 Soil Surveylogical terms soil and soil profile refer to the same Manual (Soil Survey Staff, 1951). The subdivisions ofthing.” Unfortunately, many users have consequently the C-zone (pedological C horizon) were threefold: CL,assumed that the actual profiles are different because leached and oxidized; CC, unleached and oxidized; andthe words are different. This partitioning of geological UU unoxidized and unleached.and pedological contexts was decided in an unwritten The Kay–Leighton–Frye weathering profiles were allagreement resulting from a meeting between Leighton developed to describe pedogenic horizons that they ob-and Marbut during the latter’s 1923 lectures and field served below the solum in youthful glacial deposits.trips in Illinois (Leighton, 1958). As a result, the soil and Outside glaciated regions of the world, some geologistsgeologic profile concepts were treated independently and, (and pedologists) have been using the term weatheringin many cases, differently or even mutually exclusive from profile to encompass both the pedological profile (so-each other. Hence, later concepts evolved beyond origi- lum), and the subsolum extending down to the unweath-nal intentions. ered bedrock (Pavich, 1986, 1989a, 1989b).

Quaternary geologists in the 1920s were interested insoil profiles, but considered them less important than Interdisciplinary Communication And Conceptsother geological endeavors. Agricultural geologists at

Thorp (1935, 1949; et al., 1951) was one of the firstthe time were trying to diminish or rid themselves ofto recognize the need to maintain interdisciplinary com-their dependence on geological theories and create anmunication between pedology and Quaternary geology.independent soil science, with a subdiscipline concerned

with soil genesis known as pedology. The Leighton– Robert V. Ruhe of Iowa State University and theUSDA-SCS pioneered studies combining pedology, ge-Marbut agreement was seemingly a matter of conve-

nience to delineate professional domains. This led to ology, and geomorphology (Effland and Effland, 1992).One of Ruhe’s early publications treated Kansan andviews that soil is not part of geology and vice versa.

The Leighton and MacClintock (1930, 1962) weather- Nebraskan gumbotil variability (Ruhe, 1948). His workwith Iowa State University pedologists Simonson anding profile is similar to the Kay and J.N. Pearce (1920)

profile except that the weathering zones were numbered Frank F. Riecken led him to the conclusion, initiallyproposed by Simonson (1941), that gumbotil should befrom 1 through 5. Horizon 1 was restricted to the part

called the surficial soil, the A horizon. The gumbotil recognized as part of a paleosol profile. After Ruheexamined railroad cuts in southern Iowa (Ruhe, 1954),proper, later correlated with the B(g) horizon by Simon-

son (1941) was designated Horizon 2. Horizons 3 he possessed the data necessary to develop his concepts


of landscape evolution, soil stratigraphy and soil geo- file model of the USDA has traditionally emphasizedthe solum: the A and B horizons of agricultural con-morphology that he promulgated in later works (Ruhe,

1956, 1959, 1969a, 1969b; Ruhe and Fenton, 1969). In cerns, the focus of soil survey interest. For these reasons,the subsolum C horizon has traditionally been deempha-particular, the work done by Ruhe in the Greenfield

Quadrangle (Ruhe et al., 1967) and colleagues else- sized and largely disregarded. Simonson viewed the Cin his profile concept as vague, with an “ill-defined”where in southwestern Iowa (Daniels and Jordan, 1966)

help set modern standards for integrating geological upper and lower boundary; the FAO considered the Cto be unaffected by soil-forming (pedogenic) processes.and pedological methods to obtain better results for

understanding the modern landscape, and why soils and The deep profile stratigraphic concerns of geologistsand geomorphologists led to an expanded profile devel-paleosols are where they are. In 1958, Ruhe and col-

league Raymond B. Daniels proposed revisions to the oped from, and essentially a homologue of, the pedolog-ical profile. In spite of efforts by Thorp, Ruhe and othershorizon designation system of the Soil Survey Staff

(1951) that accommodated paleosol horizons (Ruhe and to integrate them, these two approaches artificiallycreated by Marbut and Leighton, the pedological andDaniels, 1958).

Peter W. Birkeland, a Quaternary geologist influ- geological, were seen as unrelated by some practition-ers. The subsolum emphasis of the weathering profileenced by pedologist Hans Jenny when at the University

of California, Berkeley, has published on the interrela- not only applied to Quaternary deposits, but also ex-tended to deeply weathered bedrock (Pavich, 1986,tionships of pedology, Quaternary geology, and geomor-

phology (Birkeland, 1974, 1984, 1999). Birkeland modi- 1989a, 1989b; Cremeens et al., 1994).Recently, pedologists, Quaternary geologists, and soilfied the soil horizon designation system of the Soil

Survey Staff (1951) by adding a Cox for an oxidized C geomorphologists have suggested and used profile con-cepts that are synthetic, i.e., they incorporate conceptshorizon, and a Cn for unoxidized C (Birkeland, 1974).and ideas from pedology and geology—what the Ger-The latter was changed to “Cu” in 1981 in response toman scientists of the late 19th century called geopedol-the horizon designation changes of the Soil Survey Staffogy (Yarilov, 1927). When pedologists expand theirthat year (Birkeland, 1984).study of the soil profile to greater depth, they will findIn 1978, Quaternary geologist George R. Hallberg ofgeopedological profile definitions and applications use-the Iowa Geological Survey, and Iowa State Universityful. A geopedologic model can aid communication, pro-pedologists Thomas E. Fenton and George R. Millermote understanding of the whole profile to a higher leveldeveloped a hybrid profile descriptive system that incor-than the five-factor model of Jenny (1941) or currentporated notations from both the pedological and geolog-models can do, and will provide more reliable interpre-ical profiles. Letter clusters represent observed condi-tations of soil genesis and soil use. Also, as a conse-tions below the pedological solum in loess and till: e.g.,quence of a deeper view, it will attract other disciplinesOL � oxidized, leached; OU � oxidized, unleached;that, in reality, have overlapping interests with pe-and UU � unoxidized, unleached (Hallberg et al., 1978).dology.Independent of the Iowa effort, pedologist and Qua-

ternary geologist Leon R. Follmer of the Illinois Geolog-ical Survey, influenced more by Leighton’s profile ideas ACKNOWLEDGMENTSthan Frye’s, developed a fourfold division of the C hori-

This paper is part of the senior author’s Ph.D dissertationzon (Follmer, 1979, 1984) that subdivided the region and fulfills a portion of the requirements for the Ph.D. inbelow the solum and included the unweathered portion the Dept. of Natural Resources and Environmental Sciences,of the profile (Table 2). More recently, Follmer et al. Univ. Illinois at Urbana-Champaign. The authors thank the(1985) and Tandarich et al. (1994) introduced the pedo- following for assistance at various stages of the research andweathering profile concept, which contained pedogenic writing: E.A. Bettis II, S.A. Blair, S.W. Buol, H. Eswaran,

V. Holliday, H.C. Hobbs, the late I.J. Jansen, the late W.H.C and geogenic D horizons (Table 2), and integratedJohnson, E.M. Melhado, M.J. Pavich, C.W. Rovey II, L.M.the functional parts of the pedological and geologicalSabas, G.F. Vance, and L.T. West. The authors also thankprofiles.the following for translating original source materials: C.Leonhard (German), and G. Opelka and T. Chaika (Russian).

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