MARINE MARL FORMATION. 279 



full ofselenite crystals; and in the clay marl or adhesive 

 slate, occurs imbedded menilite. Marine shells occur in 

 several of the layers of the marl, and it is remarked that 

 wherever the gypsum rests immediately on the sand of 

 the marine sandstone containing shells, it contains sea 

 shells. The former bottom of the sea, however, appears 

 to have been frequently covered with a bed of white 

 marl, on which the lower beds of gypsum rest, and this 

 bed is filled with fresh-water shells. The second bed re- 

 sembles the first, and only differs from it in being thicker, 

 and containing fewer beds of marl. The only petrifac- 

 tions it contains are those of fishes ; but it encloses masses 

 of celestine, or sulphat of strontian. The third, or upper 

 bed, is by far the greatest, being in several places more 

 than sixty feet thick. It contains few beds of marl ; and 

 in some places, as at Montmorency, it lies almost immedi- 

 ately under the soil. The lower strata of this upper gyp- 

 sum contain flint, which appears to be intermixed with 

 it, and to pass into it by imperceptible gradations facts 

 which show their cotemporaneous formation. The 

 middle strata of this bed split naturally into large prisma- 

 tic concretions, with many sides. The uppermost strata, 

 of which five generally occur, and extend to a great dis- 

 tance, are thinner than the others, and are intermixed with 

 marl, and also alternate with beds of it. 



Numerous quarries are situated in this upper gypsum, 

 and which daily afford skeletons, or single bones of un- 

 known birds and quadrupeds. To the north of Paris 

 these are found in gypsum itself, where they are hard, 

 and simply invested with marl ; and to the south of Paris 

 similar remains, but in a friable state, are met with in 

 the marl which separates the beds of gypsum. Bones of 

 tortoises, and skeletons of fish, are found in the same 

 feed, and more rarely fresh-water shells of the genus cy- 



