J. CORNET,

V. THE CRETACEOUS AND TERTIARY FORMATIONSOF THE MONS DISTRICT.

By J. CORNET,Professor of Geology at tho School of Mines, Mons.

THE PALlEOZOIC FLOOR.

THE region which geologists call the "Bassin de Mons"corresponds approximately to the hydrographic basin of thelittle River Haine, which flows into the Escaut at Conde. ThePalseozoic floor presents in this region a very peculiar form,which is reflected not only in the disposition of the Cretaceousand Tertiary beds, but also in the surface-topography of thecountry. Between the source of the Haine to the east, and theEscaut to the west, the sub-Cretaceous surface of the CoalMeasures forms a long and deep valley running in an east andwest direction, that is to say, almost in the direction of thePalceozoic synclinal basin of Namur. In this valley are accu­mulated the Cretaceous and Eocene sediments which have, atthe same time, a synclinal disposition. The valley-bottom dropsfrom a height of room. above sea-level to the east of Anderlues,to om. to the south of Haine-St.-Pierre; -loom. near St. Vaast ;-250m. to the south of Havre; ---315m. at Nimy; -319m.between ]emappes and Ghlin; -327m. at Hautrages; below-394m. at Pommerceul; --333m. at Harchies (Preau) :-320m. at Bernissart ;-224m. at Thivencelles and-I25m. atOnnaing, where the valley ends. Thus it rises at both ends.

The pre-Cretaceous valley of Hainaut is certainly due, chiefly,to erosion; but it is difficult to explain it as a result of theaction of running water. It presents some characters whichrecall a glacial valley, comparable with those of certain Alpinelakes. It is not possible to enlarge on this subject here. Inorder to give an idea of the relative importance of the depressionof the valley, one may mention that at only three kilometres(less than two miles) from the point where the bottom descendsto belOW-394m. (about I,300 feet) Palaeozoic rocks of thenorthern slope of the valley outcrop at the surface at a heightof +63m. (about 200 feet). This corresponds to a slope ofabout 152 metres per kilometre (about I in 6.5). The Cretaceousrocks of the Mons Basin, which fill the pre-Cretaceous valley,overstep considerably southwards to the south of Mons and westof Dour.

With reference to the Paris Basin and the main Anglo-Franco­Belgian Basin, the Mons" Basin" is an annexe sometimes calledthe" Mons Gulf." It is connected with the main basin towardsthe Franco-Belgian frontier. It is evident that the existinglimits of the Cretaceous, both to the north and to the south ofMons, are the result of denudation, and originally the Cretaceous.

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28 J. CORNET,

beds, at least in the upper part, extended without a break northand sout h of the basin. The expression " Mons Gulf " is th ere­fore somewhat incorrect. One may add that the knowl edgeof the geology of the Mons district rests not only on surfaceobservations, but also on a study of more than 1,000 boringsand min e-shafts.

The figure (Fig. 5, page 27) represents a section of theCret aceous and Tertiary rocks of the Mons Basin , t aken throughthe t own of Mons and a t right angles to the pre-Cretaceousvalley. Pressure of space has necessit ated the diagram beingpr inted in two halves. The posit ion of the various un con­formities and the overlap of successive beds are well shown.

GENERAL TABLE OF THE TERTIARY ANDCRETACEOUS STRATA OF THE MONS BASIN.

TERTIARY-EOCENE.Paniselian.

2. Glauconitic sa nds , slightly or non-argillaceous, withthin bands of lustrous hard green grits or quartzites(with an opaline cement) containing Pinna margari­tacea, Cardita planicosta, etc.

1. Glauconitic, clayey sands with thin beds of fossiliferousargillaceous sandstone .

Locality .-Mont Pani sel, near Mons,British Equivalent.- The Paniselian is considered by the

majority of Belgian geologists as a stage intercalated betweenthe Ypresian and Bruxellian. F or others, t he Paniselian isonly a west ern facies, formed under somewhat different condi­tions, of the Bruxellian. The Bruxellian corresponds to thelowest beds, or zone of M aretia Omaliusi, of the Lutetianof the Paris Basin. In England, it has its equivalent in theBracklesham Beds.

Ypresian .2. F ine -grained, glauconitic sand, slightly micaceous.

Nummulites planulatus-elegans, Turritella hybrida,Turritella Solanderi, Xanthopsis Leachi, et c.

1. Dark blue-grey clay.Localities.-Mons, Cuesmes and Mont Panisel.British Equivalent.-The London clay.

Landenian.II. Upper Landenian (continental facies).

White sands with white sa nds tones (" gres mam elonnes"or "sarsens " ) and lent icular beds of gravel, clay andlignit e. Coryphodon eocenus, Pa chynolophus M aldani,Trionyx levalensis, Champsosaurus, Crocodilus, Lepi-

THE GEOLOGY OF BELGIUM. 29

dosteus, Amia, Eriocaulon porosum; Arundo groenlandica,etc.

Localities.-LevaJ, Grand-Reng and ]eumont.British Equivalent.-The Reading (freshwater) type of the

Woolwich and Reading Beds.1. Lower Landenian (marine facies).

6. Slightly glauconitic sand, greyish green. Gres deGrandglise with Cyprina scutellaria.

5. Glauconitic sand, dark green, with Turritella bello­vacensis.

4. Glauconitic sand, with an opaline cement (Tuffeaud'Angre), Pholadomya Konincki.

3. Argillaceous sand, calcareous and very glauconitic,often pyritous. Cyprina M orrisi.

2. Very calcareous, glauconitic sand; sandy, glauconiticmarl or a sandy, glauconitic limestone with foramini­fera.

1. Argillaceous, glauconitic sand, slightly calcareous.Lucalities.-Mons, Cuesmes, Ciply, Mesvin, S1. Symphorien,

Elouges, Angre, Grandglise. The beds I and 2 do not crop outat the surface.

British equivalents.-The Thanet Sands; and the MarineBottom-Bed of the Woolwich Series (=zone of Cyprina scutel­laria.)

Montian.II. Upper Montian (continental).

Marls, clays, lacustrine limestones and lignites. Physa,Paludina, Bithinia, Ancylus, Sphcerium, Chara, etc.

1. Lower Montian (marine or estuarine).The famous "Calcaire grossier de Mons." A friableor coherent limestone with foraminifera and Litho­thamnion. A very rich fauna with marine species,brackish-water species (Potamides, Cyrena, etc.), speciesof littoral pulmonate gasteropods (Alexia, M elampu«,Blauneria) , fresh-water species (Limncea,Physa, etc.),and terrestial species (Cyclostoma, Scarabus, etc.)

Localities.-There is now no good section.British equivalent.-None.

CRETACEOUS.

Danian.2. Tuffeau de Ciply. Soft, yellowish limestone with

grey flints. Campanile Briarti. Formerly regardedas a lateral equivalent of the Calcaire de Mons (Montian).

I. Basal conglomerate, consisting of phosphatic nodules.

30 J. CORNET,

and rernanie Maestrichtian and Senonian fossils (=Poudingue de la Malogne, pro parte).

Locality.-The quarries of Ciply.British equivalent.-None.

.Maestrichtian (sensu stricto).2. Tuffeau de St. Symphorien. Soft whitish limestone

with grey flints. Trigonosemus pectiniformis, Hemi­pneustes striato-radiatus, Thecidea papillata abundant.

I. Basal Conglomerate of phosphatic nodules (=Poudinguede la Malogne, pro parte).

Locality.-The quarry of S1. Symphorien.British equivalent.-None.

Senonian.IV. Assise de Spiennes, a Trigonosemus Palissyi.

2. Phosphatic chalk of Ciply, with flints towards the topand towards the base. Pachydiscus neubergicus, P.colligatus, Ostrea lunata, Trigonosemus elegans; Pectenpulchellus abundant. The Poudingue de Cuesmesoccurs locally at the base.

I. Chalk (" Craie grossiere") of Spiennes, with brownand black flints.

Localities.-The quarries of Ciply, Spiennes, S1. Symphorienand Baudour.

British equivalent.-The Trimingham Chalk (zone of Ostrealunata.)

III. Assise de Nouvelles, a Magas pumilus.2. Nouvelles Chalk, with Magas pumilus.I. Obourg Chalk, often with black flints. At the base

is a conglomerate with Belemnitella mucronaia and withrolled specimens of Actinocamax quadratus.

Localities.-The quarries of Harmignies, Nouvelles, andObourg.

British equivalent.-The Norwich Chalk (zone of Belemnitellamucronata).

II. Assise de Trivieres, a Actinocamax quadratus.Trivieres Chalk, without flint. Actinocamax quadratusand Inoceramus balticus. There is a conglomerate atthe base.

Localities.-The quarries of Obourg, Trivieres, St. Vaast, etc.British equivalent.-The Newhaven Chalk (zone of Actina­

camax quadratus).I. Assise de St. Vaast, a Inoceramus involutus.

St. Vaast Chalk, with mottled flints and grains ofglauconite towards the base. Inoceramus inoolutus.At the base are beds of remanie glauconite.

Localities.-The quarries of St. Vaast, etc.British equivalent.-The Dover Chalk (zone of Micraster cor­

testudinarium [Micraster decipiensJ).

THE GEOLOGY OF BELGIUM. 3I

Turonian.II. Upper Turonian.

3. Glauconitic chalk of Maisieres with Ostrea semiplana,O. canaliculata, Neoptychites peramplus and Actino­camax Strehlenensis (the Gris).

2. Marly chalk with flints (the Craie a comus of the northof France); Meuliere of Maisieres and St. Denis.Micraster Leskei (the Rabots).

I. Chalky or glauconitic marls with siliceous concretions.Micraster Leskei (the Fortes-Toises).

Localities.s-Ttxe quarries of Maisieres, St. Denis, etc.British equivalent.-The zone of Micraster Leskei and Holaster

planus, including the Chalk Rock and usually placedin England at the base of the Upper Chalk.

1. Lower Turonian.2. Whitish marls with Terebraiulina rigida (= Ter. lata?)

(the upper Dieves).Localities.-Autreppe, Hautrage, etc.British equivalent.-The zone of Terebraiulina lata.I. Clayey blue or green marls with Inoceramus labiatus,

Rhynchonella Cuvieri and Mammites nodosoides (themiddle Dieves),

Locality.-Autreppe.British Equivalent.-The zone of Rhynchonella Cuvieri and

Inoceramus labiaius.

Cenomanian.II. Upper Cenomanian.

2. Clayey blue or green marls with Actinocamax plenus(the lower Dieves).

I. Very glauconitic marls with rolled pebbles.Actinocamax plenus and Pecten asper (the Tourtia deMons).

Locality.-Hautrage.British equivalent.-The sub-zone of Actinocamax plenus

at the top of the zone of Holaster subglobosus. The lower partof the zone of Holaster subglobosus is not known in Belgium.

1. Lower Cenomanian.Marls and limestones, together with glauconitic andcalcareous sandstones with calcareous cement orchalcedonic sandstones with cherts.Schlcenbachia varians, Acanthoceras Mantelli, A. cen­omanense, Turrilites tuberculatus and Baculites bacu­loides (the upper part of the Meule de Bernissart). Thedeposits known as the Tourtia de Tournai and theTourtia de Montignies-sur-Roc, characterised by theabundance of Terebratula depressa, are a local facies.

32 THE GEOLOGY OF BELGIUM.

Localities.-Tournai (the Tourtia), Hautrage, Harchies, etc.(in coal-pits only).

British equivalent.-The zone of Schloenbachia varians withthe zone of Pecten asper ; more exactly the Cenomanian ofDevonshire of Jukes-Browne. •

Albian.East (Bracquegnies). West (Harchies, etc.).3. Sands and glauconitic 3. Calcareous sandstone, marls

sandstone with opaline and limestones more or lesscement, non-calcare- glauconitic" often with aous ; " gaize " ; conglo- chalcedonic cement andmerate at the base. with cherts. Conglomer-Trigonia dcedalea, T. ates.Elise, Cucullcea glabra Mortoniceras rostratum andand Rostellaria Par- Inoceramus sulcatus (thekinsoni (the Meule middle part of the Meule dede Bracquegnies). Bernissart.)

Localities.-Bracquegnies and Thieu.British equivalent.-The zone of Mortoniceras rostratum.

and the Greensand of Blackdown exactly.2. Sand and glauconitic calcareous sandstone, limestones

and grey calcareous sandstone, clay and conglomerates.Hoplites interruptus and Inoceramus concentricus (thelower part of the Meule de Bernissart).

Localities.-In coal-pits only.British equivalent.-The zone of Hoplites interruptus?

1. Sands and coarse sandstones, glauconitic or ferruginous,and conglomerates (the base of the Meule de Bernissart).

Localities.-In coal-pits only.British equivalent.-The zone of Douvilleiceras mammillatum?

Wealden.Various clays (including fire clays, etc.), sands and sandstones;

pebble-beds and conglomerates; lignites and limonite. Igu­anodon bernissartensis, I. Mantelli, Goniopholis simus, Oligo­pleurus vectensis, Cyrena Tombecki, CedrusCorneti, Pinus Briarti,Cycadites Schachti, Sphenopteris Fittoni and Weichselia Mantelli.

Localities.-Bernissart (in a coal-pit), Hautrage, Villerot,Baudour, Maisieres, Thien, etc.

British equivalent.-The Wealden.

[For further details see Comet and Briart (for Cretaceousand Montian) Bull, Acad. r, Belgique, 1865-7-70-7 ; F. L.Cornet (Upper Cretaceous) Q.J.G.S. 1886; J. Cornet (Turonian)A nn. Soc. geo': Belgique, 1919 ; J. Cornet (general) , Geologie,'vol. I., Mons, Ig09.-L.D.S.]