19S On Formations, [March, 



Mont Martre. There we observe three masses of gypsum. 

 First Mass. Rests on the limestone. The lowest part is com- 

 posed of alternate thin beds of gypsum, including crystals of 

 iselenite, and solid calcareous marl, and very thin slaty clay marL 

 In the gypsum large lenticular crystals of gypsum occur, and iii 

 the marl menelite. The gypsum contains sometimes ^'resh water, 

 sometimes marine ^halh.— Second Mass. In this mass the strata 

 of gypsum are thicker than in the preceding, and the beds of 

 Hiarl less numerous. In the clay marl petrified fishes occur, and 

 also masses of sulphate of strontiao. — Third Mass, This is the 

 thickest of the three masses, being in some places 30 metres 

 thick. It contains but few beds of marl. The lowest strata of 

 this mass contain silex impregnated with the gypseous matter. 

 The intermediate strata are divided into large columns. The 

 Tapper beds are penetrated with marl, and also alternate with it» 

 It contains in general five beds of marl. It is in this third mass 

 that the remains of unknown quadrupeds and birds are found. 

 To the north of Paris these petrifactions occur m the gypsum 5 

 but to the south, often in the beds of marl that alternate with the 

 gypsum. This gypsiun also contains bones of the tortoise, and 

 skeletons of fish, and also fresh water shells. This third mass is 

 essentially characterised by the presence of the skeletons of 

 quadrupeds. These remains serve to determine it when it occurs 

 isolated, for no such remains have hitherto been found in the 

 lower mnsses. Above the gypsum occur thick beds of calca- 

 reous and argillaceous marls. It is in the calcareous marl that 

 we meet wiih trunks of palm-trees penetrated v^ith silica. In 

 the same beds there occur shells of the genera planorbis and 

 limneus, that scarcely differ from those that live in our marshes. 

 These petrifactions are alleged to prove that these marls are of 

 fresh watt-r origin, like the gypsum on which they rest ; and it 

 is remarked that the gypsum, t!ie beds of marl that occur in 

 it, and those that cover it, constitute the first or oldest fresh 

 wat^r formation of the Parisian series of rocks. Above these 

 marls we observe numerous and often thick beds of argillaceous 

 and calcareous marls. They contain no petrifaction, and the 

 formation to which they belong has not been determined. Above 

 these we meet with a yellowish slaty marl, which towards its 

 lower part contains bails of sulphate of strontian, and a little 

 above a thirs bed of small bivalve sliells belonging to the genus 

 cytherea. It 's said that it serves as the liuiit of the fresh water 

 formation, and mark the beginning of a new marine formation. 

 In shon, all the shells we find above it are marine. It is about 

 a metre tiiickj and contains in its upper layers also cerites, spi- 

 robes, and bones of fi-^h. Over tiiis rests a thick bed of green 

 marl. It contains no pciiifiction?, but nodula of sulphate of 

 strontian. Pour or five beds of rna; 1 succeed tlie green marl, 

 £ind appear to contaiu no petrifactions^ but these beds are covered 



