Toward a Comprehensive Soil Classification System

Charles W. Finkl

Institute of Coastal Studies Nova University

INTRODUCTION

The rapid growth of specialized disciplines, as seen in the natural sciences over the last several de­cades, has fostered new and diverse vernaculars. As new information is gained from closer study of natural realms, additional terms are needed to describe an increasing array of recorded phenomena. Advances in the geological sciences have, for ex­ample, contributed to a burgeoning vocabulary. The 1980 edition of the Glossary of Geology (American Geological Institute) contains 36,000 terms, about 3,000 more than the 1972 edition . These additions reflect changes in the geosciences over the last decade, especially advances in fields dealing with plate tectonics, remote sensing, igneous petrology, paleomagnetism, and biostratigra­phy. Many recently coined terms are appropriate and useful. Others will not stand the test of time and will fade away. Soil scientists as a col­lective body are perhaps also falling unwittingly into a morass of scien­tific jargon. This terminological bot­tleneck is particularly evident in the field of soil classification where there exists a multiplicity of terms for de­scribing soil units. This situation presents an imposing problem for geographers in particular, but geol­ogists, ecologists, and environmen­tal scientists also have cause for concern.

The development of new soil classification systems and revisions of old ones is a global phenomenon (1), not a local situation where one or two nations have brought up­dated versions on line. The revolu­tion that is taking place in soil clas-

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sification probably will continue. Just how well geographers and others cope with a multitude of soil tax­onomies may depend on their abil­ity to rationalize cultural overtones in the scientific arena.

CHANGING TAXONOMIES

In the early part of the 20th cen­tury, physical geographers and soil scientists shared many common in­terests. Both groups investigated with equal vigor the relationships be­tween soils, landforms, and vegeta­tion. Results of research focusing on problems of soil erosion, conserva­tion, soil mapping, land use, archae­ology, and geography appeared in geographical journals as well as in the soil science literature (2) . Curtis Fletcher Marbut, Chief of the Soil Survey Division of the U.S. Depart­ment of Agriculture for many years, was also a founding member and a president of the Association of American Geographers (1924-1925). Such close ties between the two disciplines left a legacy of scientific terminology in the United States that was comprehensible to both parties. Much of that changed, however, with the publication of Soil Taxonomy (3) in 1975, the new official soil classi­fication system for the United States Department of Agriculture. Podzols, Gray Wooded soils, and laterites were respectively replaced, in part, by great groups of Spodosols (Cryorthods, Fragiorthods, Haplor­thods) , Alfisols (Eutroboralfs), and Oxisols (Acrorthox) . Many of the principal old terms, which were de­rived from folk names indicative of some distinctive property of the soil, were dropped. Podzols, for exam-

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pie, were widely known as acid ashy gray sands over dark sandy loams, the name being derived from the Russian terms pod (beneath) and zol (ash) . They were supplanted by new names intended to be more precise and meaningful. To American soil scientists that change-over was a gradual process involving several experimental approximations (4) that preceeded the present version pub­lished as U.S.DA Handbook No. 436 (Soil Taxonomy).

Many geographers were un­doubtedly jolted by the complexity of Soil Taxonomy and the appar­ently rapid phase-out of older sys­tems. The loss of a familiar pedo­logical terminology, which had gained wide acceptance, lead some to think that it was easier to "fight than switch" (5) . Soil scientists have lauded the merits of Soil Taxonomy but in spite of their efforts to con­vince other professionals that it is easier to "switch than fight" (6), there is still resistance to change. Even though there have been numerous attempts to i ntroduce the new American system of soil classifica­tion in palatable form (7), many have found terms like Grossarenic Pa­leaquult, Pachic Ultic Haploxeroll, and Paralithic Vertic Ustrochrept to be cumbersome and distasteful. To some, these terms do not sound the way names of soils should sound, but this is hardly a valid criticism of the system. Questions like "What is wrong with names like Chernozem, Podzol, Rendzina, Andosol, and bog soil, anyway?" remain common among those outside of the soil fraternity . Most geographers and geologists still retain a basic notion

as to what these terms mean, or at least they think they do. With time comes change and hopefully some degree of progress. So, if American geographers just learn the new soil taxonomy, all will be right with the world , i.e., with the world of soil.

THE CHALLENGE OF NOMENCLATURE AND SOIL

CORRELATION

For scientists working primarily in the United States and for those who do not require much detailed infor­mation about so ils elsewhere, the new soil taxonomy will meet their needs. The situation becomes less comfortable however, when global or regional soil patterns are relevant to, or indeed the very object of, study. The investigation of soil dis­tributions from an intercontinental point of view or even on an inter­national basis can be a nomencla­tural challenge that wears down the grit of even the most hardy.

Consider for a moment the com­plexity of the situation facing to­day's geographers. Serious regional studies of North American soils must eventually deal with the different systems employed by the United States (1), Canada and Mexico (8) . Most countries in South America apply the FAO/ UNESCO legend al­though some nations such as Brazil (9) have their own independent soil taxonomy. In Western Europe the situation is rather more complex where England and Wales (10), West Germany (11), and Belgium (12) , for example, each have a different sys­tem of soil classification. In France, two systems are frequently applied (13) . Russian systems of soil classi-

fication (14) apply to most of north­ern Asia while other taxonomies are applied in southern Asia, the Indian subcontinent, and the Far East (15). Australia , unlike most developed countries, does not maintain a na­tional soil survey. The Northcote classification (16) is applied on a continental basis although names of soils from previous systems can still be used. The Northcote system is alpha-numerical but it is sometimes more convenient to discuss a partic­ular calcareous red earth than a Um 5.51 principal profile form. Several taxonomic systems are in force on the African continent making it a real potpourri of soil classification . The French system, with modifica­tions, is still widely used in parts of equatorial Africa and in some of the former colonies. The FAO/ UNESCO legend is followed throughout much of the Middle East and a few nations such as South Africa have distinc­tive soil taxonomies of their own (17). Still other countries (e.g ., Costa Rica and Venezuela) retain vestiges of the former U.S. system. Even is­land nations such as New Zealand (18) and Japan (19) have indepen­dent national soil taxonomies.

Although the FAO/ UNESCO soil legend is followed in many parts of Central and South America, and also parts of Africa, it is not, strictly speaking, a classification system. It is mainly used as a guide in the preparation of soil maps. Of the many world soil maps that are avail­able, perhaps the best known are those prepared by the U.S. Soil Con­servation Service (SCS) and FAO/ UNESCO. The SCS world maps are usually seen at textbook scale,

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whereas the FAO sheets are printed at a scale of 1:5,000,000.

It should also be noted that there are about as many special soil clas­sification schemes (20) as there are concepts of soil (21). Most special purpose classifications focus on some inherent pedological property such as salinity, mineralogy, soil re­action (pH), and micromorphology; or they consider selected attributes having practical significance to en­gineering or some other practical field such as pedogeochemistry. Re­gional classifications have been de­veloped for polar and equatorial soil zones (22) because these soils are quite different from mid-latitude va­rieties which constituted the taxo­nomic data base for many systems.

Such a number of soil classifica­tion systems understandably leads to confusion, befuddlement, and even rage on the part of those trying to make comparative studies. Spe­cialists who pttempt to determine equivalence between soil units, fre­quently find the job to be of night­marish proportions because so few terms are synonymous.

DISCUSSION

The decision to adopt one tax­onomy as "the system" for describ­ing the world's soils might be a sat­isfying gesture to a particular interest group, but it hardly meets the need for a universal or comprehensive system. Classification systems have been developed in the geological, biological, and botanical sciences which permit a rational taxonomical organization of rocks, animals, and plants (23). The unique properties of soils, which are due to many fac-

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tors, have apparently slowed the de­velopment of a comprehensive clas­sification . Soil Taxonomy perhaps comes closest to a basic system and has received some degree of inter­national recognition. Hierarchical systems of this kind, however, risk excessive proliferation of classes and at the same time seem to lack ac­commodation for intergrade soils (24). Other reviewers (25) have cri­ticised the system on the basis of its style of classification, narrowly de­fined classes, and attempts to rec­oncile the concept of polypedons with the lack of discrete soil entities in nature. Other problems concern the classification of polygenetic soils, especially those with pedogenic dis­continuities occurring within 50 cm of the surface. The classification of profiles (pedons) containing buried soils, multisequal soils, is trouble­some because soil-stratigraphic se­quences are more common than generally believed (26). Some clas­sifications make specific provision for polygenetic soils (27). Only time will tell whether this scheme or some subsequent revision will become a comprehensive world system.

In the meantime, geographers can follow an eclectic approach applying some system of their choosing to the world scene or they can become polydexterous using local systems wherever their work takes them. Both choices involve aspects of soil cor­relation and much expertise in the field of soil classification. The prob­lem is not one of merely changing names on map legends because the terms are frequently not equivalent and hence map boundaries also must be changed to reflect the new ter-

minology . Consideration of one common soil group, the brown pod­zalic soils, illustrates some of the difficulties involved . Brown podzolic soils of the revised 1938 U.S. clas­sification are approximately equiva­lent to Cryandepts, mesic families of entic Fragiorthods and Haplorthods and less so with Dytric Eutrochrepts, Dystrochrepts, and Frgaiochrepts of Soil Taxonomy. Approximate corre­lations with other systems are Sol ocre-podzolique (French system , 1965), Leptic Podzol (FAD), Podzolic Brown Earth (England and Wales), and Brown Podzolic soil (Australia) . Tables indicating relationships of soils in Soil Taxonomy give a some­what different approximate equiva­lent from the French taxonomy (p. 440) to the current U.S.D.A. sys­tem, viz., Sols-ocre podzoliques are indicated as being more or less equivalent to frigid and mesic fam­ilies of entic subgroups of Haplor­thods, a rather more specific asso­ciation than previously given (p. 433). Thus, correlation of soil units re­quires detailed knowledge of soil descriptions, class limits, and appli­cability of those definitions to exten­sions in widely separated natural environments. Some surveys still employ parts of the revised 1938 U.S.DA classification and it is gen­erally not possible to equate those great soil groups exactly with cur­rent great groups. In a few words, taxonomic names are not inter­changeable from one system to an­other because concepts of soil are modified as taxonomies evolve.

A partial solution to the problem of multiple classification systems and associated terminologies might in-

clude emphasizing aspects of soil formation . A unified concept of pedogenic regimes might help iden­tify the main geographic zones or physiographic regions dominated by specific soil-forming processes. Areas where certain processes are domi­nant would include, for example, zones of podzolization, lateritization, gleization, calcification, and salini­zation . Regions could then be stud­ied in terms of pedogenic zonation or in terms of soil-process interre­lationships with other natural (rocks, vegetation, climate) or cultural (set­tlement patterns, resource utiliza­tion) phenomena.

The global distribution of soils has been depicted using many dif­ferent classification schemes. De­ployment of a comprehensive inter­national soil taxonomy would do much to alleviate existing con ­straints imposed by so many clas­sifications. The diversity of soil tax­onomies and the regions where they are used suggests the possibility of studying a "geography of soil clas­sification." With few exceptions, soils throughout the world are not so dif­ferent that each requires a unique classification . All soils should theo­retically fit into a comprehensive open-ended scheme. Is the prolifer­ation of soil classifications that we see today the result of scientific ef­forts to discover the best system, or could it be partly the result of sys­tems that reflect a certain degree of national pride and cultural heritage?

CONCLUSION

The development of independent soil classifications by national sur­veys has led to a classificatory di-

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lemma. As the number of systems increase, so does t he jargon and tha t st ul ti f ies p rog ress when it reaches overwhelm ing proportions. When the re are approx imately a dozen major pedologica l class if ica­t ions used to identify the same nat­ural entity there is ca use for concern and, indeed, a desire for simpl ifica­t ion. The development of a univer­sal , comprehensive soil classifica­tion w i ll requ i re greate r un ­derstanding of soil systems and, perhaps more important ly , con ­certed international cooperation. Unti l a comprom ise is reached and a comprehensive taxonomy is accept­able, geographers and other geo­scientists must wade very carefully through a variety of classifications.

NOTES

1. In 1975 the Soil Conservation Service introduced Soil Taxonomy, a new system of soi l classif ication (U.S. Dept. Agric. Hndbk No. 436) replacing Baldwin, M., Kel­logg, C. E., and Thorp, J., " Soil classificat ion," in Ham· ibidge, G. (ed.), Soils and Men, U.S. Dept. Agric. Year­book 1938, pp. 979-1000; and revisions by Riecken, F. F. and Smith, G. D., "Lower categories of soi l classif i­cation : Family, series, type, and phase," Soil Science, Vol. 67 (1949)' pp. 107-115, and by Thorp, J. and Smith, G. D., " Higher categories of soil classification : Order, suborder, and great groups," Soil Science, Vol. 67 (1949), pp. 117-126. For a discussion of modern classification schemes and the history of their development leading to new and revised taxonomies. see Buol . S. W., Hole. F. D" and McCracken, R. J., Soils Genesis and Classifi­cation (Ames: Iowa State Un iversity Press, 1980), pp. 194-224. In addit ion to the systems of national or co­operative soil surveys, there are other genera l classifi­cations, e.g. FitzPatrick, E. A., Pedology (Edinburgh : Oliver and Boyd, 1971 ), p. 306; as well as specialized systems such as those dea ling with the organization of organic soil materials, e.g. Ba l, L. , Micromorphologica l Analysis of Soils (Wageningen, The Netherlands: Soil Survey In­stitute), p. 174; and pedograph ic studies involving mi­cromorpholog ica l classification of inorganic materials, e.g. Brewer, R., Fabric and Mineral Analysis of Soils (New York : Wiley, 1964), p. 470 and Brewer, R., " Rela­tionship between particle size, fabric and other factors in some Australian soils," Ausr. Jour. Soil Science, Vol. 17 (1979), pp. 29-41 .

2. Examples of common interest include : Marbut, C. F" " Soils of the Great Plains," Annals Assn. Amer. Geogr., Vol. 13 (1923), pp. 41-66; Shantz, H. L. and Marbut, C. F .. "The vegetat ion and soi ls of Africs," Amer. Geogr. Soc. Research Series No. 13 (1923, pp. 1-263; Walther, J., " Das geo logische Alter und die Bildung des Laterits." Petermanns Milt., Vol . 62 (1916), pp. 1-7 and 46-53 ; and

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more recently Ganssen, R.. Bondengeographie (Stutt­gart: Koehler, 1957), p. 219; Eyre, S. R., Vegetation and Soils (Chicago: Aldine, 1963), p. 324; Bunting, B. T., The Geography of Soil (Ch icago : Ald ine, 1965), p. 213. Two recent attempts to incorporate the new terminology of Soil Taxonomy in geograph ical studies include text­books by Steila, D., The Geography of Soils (Englewood Cl iffs, NJ : Prentice-Hall, 1976), p. 222 and Foth, H. D. and Schafer, J. W., Soil Geography and Land Use (New York : Wiley, 1980), p. 484.

3. Soil Survey Staff, Soil Taxonom y: A Basic System of Soil Classification for Making and Interpreting Soil Sur· veys (Washington, D.C.: U.S. Government Printing Of­fice, U.S.D.A. Handbook No. 436, 1975), p. 754.

4. Soil Survey Staff, Soil Classification, A Comprehensive System, 7th Approximation (Wash ington, D.C.: U.S. Government Printing Office, 1960) p. 503; Soil Survey Staff, Supplement to Soil Classification System (Wash­ington, D.C.: U.S. Government Printing Office, 1967), p. 207.

5. See for example the discussion in C. B. Hunt, Geology of Soils (San Francisco: Freeman, 1972), pp. 18(}-183.

6. M. G. Cline, " Log ic of the new system of soil classifi­cat ion," Soil Science, Vol. 96 (1963), pp. 17- 22 ; C. E. Kellogg, " Why a new system of soil classification," Soil Science, Vol. 96 (1963), pp. 1- 5; S. W. Buol, F. D. Hole, and R. J. McCracken, Soil Genesis and Classification (Ames: Iowa State University Press, 1973), pp. 18(}-181.

7. C. W. Finkl, " Geographers, pedologists, and the new sys­tem of so il classification : A commentary for geogra­phers," Prof. Geogr. , Vol. 19 (1967), pp. 239-243; D. Steila, The Geography of Soils (Englewood Cliffs, NJ: Prentice-Hall , 1976), p. 222.

8. FAO/ UNESCO Staff, Soil Map of the World, Vol. I, Leg­end (Paris: UNESCO, p. 59; National Soil Survey Com­mittee of Canada, The System of Soil Classification for Canada (Ottawa : Canada Department of Agricu lture, 1975), p. 255; J. S. Clayton, W. A. Ehrlich , D. B. Cann, J. H. Day, and I. B. Marshall, Soils of Canada, Vol. I, Soil Report (Ottawa : Canada Department of Agriculture, 1977), p. 243; Martini, J. A .. " Principales grupos de suelos de America Central y Mexico," Fititecnia Latinoamericanan, Vol. 4 (1967), pp. 57-79.

9. J. Bennema, "Report to the government of Brazil on the classification of Brazilian soils," FAD Report No. 2197, p. 83.

10. B. W. Avery, " Soil classificat ion in the Soil Survey of England and Wales," Jour. Soil Science, Vol. 24 (1973), pp. 324-338.

11 . E. MOckenhausen, F. Kohl, H. P. Blume, F. Heinrich, and S. Miiler, Entstehung, Eigenschaflen und Systematik der Boden der Bundesrepublik Deutschland (Frankfurt : DLG­Verlag, 1977).

12. R. Tavernier and R. Marechal, " Soil survey and soil clas­sif ication in Belgium," 7th Internall. Congr. Soil Sci. Trans., Joint Mtg. Comm. IV & V (1962), pp. 296-307.

13. G. Aubert, " La classification pedolog ique util isee en France," Pedolog ie, Spec. No. 3 (1965), pp. 25-51 ; P. Duchaufour, Ecological Atlas of Soils of the World (New York : Masson, 1978), p. 178.

14. N. N. Rozov and E. N. Ivanova, " Classification of the soils of the USSR," Soviet Soil Science, Vol. 2 (1967), pp. 147-156; E. N. Ivanova and N. N. Rozov, Classifica­tion and Determination of Soil Types (Wash ington, D.C.: National Science Foundation, 1970), p. 271 .

15. S. P. Raychaudhuri and S. V. Govindarajan, "Soil gene­sis and soil classification," in Review of Soil Research in India (New Delhi : Indian Council of Agricultural Re· search, 1971), pp. 107-135; L. T. Hai, Soils of Taiwan (Taipei : Society of Soil Scientists and Feni lizer Technol­og ists of Taiwan, 1962).

16. K. H. Nonhcote, "A factual key for the recognition of Australian soils," C.S.I.R.O. (Australia) Division of Soils, Div. Repon 4160 (1960); C. G. Stephens, A Manual of Ausrralian Soils (Melbourne : C.S.I.R.O., 1962). p. 48; H.C.T. Stace et ai, A Handbook of Ausrralian Soils (Glen­side, South Australia: Rellim, 1968', p. 435.

17. C. R. van der Merwe, Soil Groups and Subgroups of Sourh Africa (Pretoria: Government Printer, 1962). p. 355; C. N. Macvicar, Soil Classificarion (Pretoria : De­panment of Agricultural Technical Services, 1977), p. 150.

18. N. H. Taylor, " Soil survey and classification in New Zea­land," Proc. 7rh Pacific Sci. Congr .. Vol. 6 (1949), pp. 103-113; N. H. Taylor and I. J. Poh len, " The classifica­tion of New Zealand soils," in Soils of New Zealand (Lower Hun: New Zea land Depanment of Industrial Re­search, in press). The Soil Bureau is also considering adopting Soil Taxonomy as the official system for the national survey.

19. See for example Y. Kato, " Some discussions on the cat­egories of Japanese soil classif ication," Pedologis r (To, kyo), Vol. 21 (1977" pp. 2-18.

20. See summaries in Finkl , C. W. (ed.', Soil Classificarion (Stroudsburg, PA: Hutchinson Ross, in press', Bench­marks in Soil Science Series, Vol. 1. Examples of spe­cial ized soil classifications include : Arkley, R. J ., " Factor analysis and numerical taxonomies of soils," Soil Sci· ence Soc. Amer. Proc., Vol. 35 (1 971 ), pp. 312- 315; As­phalt Institute Staff, Soils Manua l fo r Design of Asphalr Pavemenr Srrucrure (Houston : Asphalt Institute, 1969; Barran, B. C., "A revised classification and nomenclature of microscopic soil materials with particular reference to organ ic compounds," Geoderma, Vo l. 2 (1969) , pp. 257- 271 ; Brazilevich, N. I. and E. I. Pankova, " Classifi­cation of soils according to their chemistry and degree of salini ty," Agrokem Talajr, Vol. 18 (1 969), pp. 219-226 ; Burmister, D. M., " Identif ication and classification of soils," ASTM Spec. Tech. Publ. No. 113, pp. 3-24; Cas­agrande, A .. " Classification and identification of soils, " Proc. Amer. Soc. Civil Engr., Vol. 76 (1947), pp. 783-810; de Bakker, H. and J . Schelling, Sysreem van bodemclas­sificarie voor Nederland (Wageningen, The Netherlands : Soil Survey Institute, 1966), p. 217 ; Forest Soils Division Staff, " Classification of forest soils in Japan," Bull Govr. Foresrry Exper. Sra. (Tokyo), Vol. 280 (1975), pp. 21-28; Hubrich, H .. "The classification of soil types according to hydrolog ical characterist ics:' Arch iv. f. Acker-und Pflanzenbau & Bodenkunde, Vol. 17 (1973). pp. 795-805.

21 . C. W. Finkl, "Soil," in R. W. Fairbridge and C. W. Finkl (eds.). Encyclopedia of Soil Science, Pan I (Stroudsburg, PA: Dowden, Hutchinson & Rossi Academic Press, 1979), pp. 433-435.

22. J. C. F. Tedrow, " Systems of polar soil classification:' in Soils of Polar Landscapes (New Brunswick, NJ : Rut­gers University Press, 1977) pp. 114-135; E. C. J. Mohr and van Baren, " Classification of tropical soils," in- Trop­ical Soils (The Hague: Uitgeverij W. van Hoeve, 1959). pp. 472-489; Buringh, P., Imroducrion ro rhe Srudy of Soils in Tropical and Subrropical Regions (Wageningen, The Netherlands: Center for Agricultura l Publishing and Documentation, 1979), p. 146; Oyama, M., " A classifi­cation system of paddy rice field soils based on their diagnostic horizons," Bull. Nar/. Insr. Agric. Sciences, Vol. 12 (1962), pp. 303-372.

23. For examples of effons toward development of compre­hensive classification systems see : Crowson. R. A., etas· sificarion in Biology (Chicago: Aldine, 1970). p. 350; Hedberg, H.D. Inrernarional Srrarigraphic Guide (New York: Wiley, 1976), p. 200; Mayr, E .. Principles of Sys­remaric Zoology (New York: McGraw-Hili, 1969). p. 428 ; Pettijohn, F. J. , " Classification of sandstones," Jour. Geol .. Vol. 62 (1954), pp. 360-365; Simpson, G. G., Prin­ciples of Animal Taxonomy (New York : Columbia Uni­versity Press, 1961 ). p. 247 ; Stoll, N. R. (ed.), Imerna­riona l Code of Zoolog ical Nomenclarure (London : International Trust for Zoological Nomenclature, 1964), p. 176; Streckeisen, A. L., " Classificat ion and nomencla­ture of igneous rocks (final repon of an inquiry):' Neues Jahrbuch f. M ineralogie, Abhandlungen, Vo l. 107 (1967), pp. 144-214.

24. Butler, B. E .. Soil Classificarion for Soil Survey (Oxford: Clarendon, 1980), p. 129.

25. FitzPatrick, E. A .. Pedology, A Sysremaric Approach ro Soil Science (Edinburgh ; Oliver & Boyd, 1971 ), p. 306; Jones, T. A., " So il classification-a destructive criti· cism:' Jour. Soil Science, Vol. 10 (1950), pp. 195-200; Knox, E. G., " Soil individua ls and soil classificat ion," Soil Sci. Soc. Amer. Proc., Vol. 29 (1 965), pp. 79-84.

26. Soil stratigraphy is a specialized field which deals w ith the superposition of soil profiles. Soil-stratigraphic stud­ies combine stratigraphic principles and practices with pedolog ical techniques in attempts to resolve complex­ities of layered soil sequences. For funher information see Morrison, R. B .. " Principles of Ouaternary soil stra­tigraphy," in Morrison, R. B. and Wright, H. E. (eds.), Ouarernary Soils (Proc. VIIINOUA Congr.), Vol. 9 (1967), pp. 1- 69 ; and Finkl, C. W .. " Stratigraphic principles and practices as related to soil mantles: ' CATENA. Vol. 7 (1 980), pp. 169-194.

27. For example, Duchaufour, P., Ecological ArIas of Soils of rhe World (New York : Masson, 1978), p. 178; FitzPatrick, E. A .. " Soil nomencl ature and classification," Geoderma, Vol. 1 (1 967), pp. 91 - 105.

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