THE REVOLUTIONS OF THE CRUST OF TfTE EARTH. 307 



white of marble, of chalk and of the calcareous formations would be 

 impossible without the intervention of organisms,* Marine water con- 

 tains about 3.5 per cent, of salt, of which the sulphate of lime consti- 

 tutes 4.G17 per cent. A thousand parts in weight of marine water 

 contains, then, 1.07 parts of sulphate of lime or of gypsum. Eeckoning 

 the mean depth of the sea at 2,000 meters, this quantity will correspond 

 to 1,070,000,000,000 of kilograms (1,040,000,000 tons), and the specific 

 gravity of gypsum being equal to 2.9, the total volume of this material 

 will be represented by 578,000,000,000 of cubic meters (751,000,000,000 

 cubic yards). This quantity is greater than the mass of all the calcareous 

 rocks of the continents, and sufBcient material is aiibrded by it for the 

 formation of new calcareous rocks. But as the carbonate of lime is not 

 found in considerable quantities in marine water, and as the gypsum 

 is the only calcareous comi)ound so distributed, we must look for the 

 source of the carbonate of lime, which is the chief constituent of the 

 shells and the carapaces of marine animals. According to the various 

 investigations in regard to this matter, plants decompose the gypsum, 

 the sulphur of which serves la the formation of the albumen, the 

 principal aliment of animals. The lime contained in the cells of the 

 alimentary plants is put in circulation by the digestion of these plants, 

 and after having contributed to the purification of the nourishing liquid 

 which it deprives of its carbonic acid, it is secreted and forms the shells 

 and the carapaces. 



Among all the marine animals the smallest are the Infusoria, and 

 especially the BJiizopodes, which contribute mostly to the formation of 

 the calcareous strata. 



The other organized deposits, particularly those which proceed from 

 the debris of the Testacca, are formed for the most part along the sea- 

 coast and principally upon the flat, sandy, muddy shallows, or very 

 slight inclinations of quiet gulfs.t After the death of the shell animals 

 the disengagement of the gas consequent upon their decomposition 

 renders them specifically lighter, so that the constant play of the waves 

 throws them readily either upon flat shores, where they are liiled up 

 with their shells unbroken, or upon steep cliffs, where the continual 

 shock of the water reduces them to consolidated masses of debris which 

 constitute the shell-marl. Submarine banks covered with Testacea of 

 the genus Ostrea are constantly raised by the remains of these animals, 

 while at the same time they gain in extent by the accumulation of the 

 shells which fall from the bank and gradually fill up the surrounding 

 depths. 



The sand and clay transported by the rivers are generally the products 

 of siliceous rocks and of the trituration of their debris encountered in 

 the beds of rivers under the form of pebbles and gravel. The two 



' Mohr, Keue Ansicht iiber die Entstehung tier Kalkgehirge, Niederrhein. Sitzungsberichte, 

 t. xxii, pp. 65, 99. 



t D'Archiac, Cours dc Paleontologie Stratigraphiquc, t. ii, p. 304. 



