in the Mediterranean. 61 



The result of these analyses sufficiently shews the remarkable re- 

 semblance that prevails, in respect to their composition, between the 

 shells petrified in geological times, and those petrifying in the Medi- 

 terranean. The small quantity of animal matter contained in both 

 is pretty nearly the same ; shells recently petrified offer only a slight 

 excess over fossil species, which, however, is never considerable. 



The phosphate of lime existing in certain of these shells in a living 

 state, such as the Oysters, Pectens, and Venus, is not found in petri- 

 fied shells, whatever be their date. This peculiarity perfectly ac- 

 cords with the geological observations mentioned above. 



It will be remarked, finally, that all the shells examined contain 

 sulphate of lime. Although this salt is found in pretty considerable 

 proportion, it had not been indicated in the analyses of oysters, as 

 given by Vauquelin, Bucholz, and Brandex. The existence of this 

 earthy salt cannot, however, be doubted ; for if we calcine the shells 

 of Oysters, Pectens, and Venus, and dissolve the residue of this cal- 

 cination in chlorhydric acid, the liquor will discharge sulphuretted 

 hydrogen in abundance. 



Of the Shellt/ Sandstones now forming in the Sfediterranean. 



We ought, in conclusion, to direct attention to those shelly sand- 

 stones, which we observe in our own day on the shores of the Mediter- 

 ranean, and which we have already referred to as representing the 

 analogues of the shelly sandstones met with in such abundance in 

 geological formations, particularly of the tertiary epoch. 



It often happens that the sands of the Mediterranean, when they 

 become cemented together, incorporate in their masses a great number 

 of shells in a more or less advanced state of petrifaction, and thus 

 form true banks of shells. These modern shelly sandstones differ 

 from the shelly sandstones peculiar to the geological formations only 

 in their small extent. They are found disseminated in the midst of 

 sea-sands, forming scattered insulated blocks, without continuity, and 

 at very unequal distances. 



It has appeared to us interesting to ascertam the nature of the 

 gluten which gives adherence and solidity to these sands, and which 

 produces the numerous arenaceous agglomerations the sea throws up 

 on its shores. By separating the shells and their debris from these 

 shelly rocks, and treating them with chlorhydric acid, which dissolves 

 the smallest detritus of the shells not separated by mechanical means, 

 a residuum remains, which presents the physical qualities of clay. 

 This kind of mineral gluten, then, is analogous to Roman cement ; 

 like it, it is very plastic, and hardens and solidifies under water. Wo 

 may add that a clay quite analogous, and which produces the same 

 effects, is found on the shores of the ocean, principally on the coasts 

 near Havre, where one of us observed it. 



Although these shelly rocks are found on the shores only in small, 

 and almost always insulated masses, it is yet probable that they con- 



