318 GEOLOGIC TIME. 



liarity of vsea water in t;ikiiij>- ui) a large amount of aniorplious carbon- 

 ate of lime and throwing it out in crystalline form accounts for the 

 filling up of tbe interstices of massive coral with crystalline carbonate 

 in coral islands and other calcareous formations, so that all traces may 

 ultimately be lost of the original organic structures.* 



The authors explain the disappearance of shells and lime deposits in 

 the greater depths of the ocean by their being dissolved by the carbonic 

 acid in tlie water, which is present in larger quantity at great depths, 

 and also is produced by the decomposition of the animal matter of the 

 shell and of the various organisms living in the water and on the bot- 

 tom. They conclude that — 



"On the whole, however, the quantity of carbonate of lime that is 

 secreted by animals must exceed what is redissolved by the action of 

 sea water, and at the jn-esent time there is a vast accumulation of the 

 carbonate of lime going on in the ocean. It has been the same in the 

 past, lor with a few insignificant exceptions all the carbonate of lime in 

 the geological series of rocks has been secreted from sea water and 

 owes its origin to organisms in the same way as the carbon of tlie car- 

 boniferous formations; the extent of these deposits api)ears to have 

 been increased from the earliest down to the present geological period." t 



In their report on deep sea deposits, collected by the Challenger expe- 

 dition, Messrs. Murray and Renard state that the chemical products 

 formed in hUu on the floor of the ocean nearly all originate in a sort of 

 broth or ooze, in which the sea water is but slowly renewed. Many of 

 them appear to be formed at the surface of the deposit — at the line 

 separating the ooze from the superincumbent water, where oxidation 

 takes place. In the deeper layers of the deposit a reduction of the 

 higher oxides frequently occurs, and at the surface of the mud or 

 ooze there are many living animals as well as the dead remains of sur- 

 face plants and auimals.| They also conclude that practically all the 

 carbon of marine organisms must ultimately be resolved into carbonic 

 acid. The quantity of that acid produced in this way must be enormous, 

 and can not but exert a great solvent action not only on the dead cal- 

 careous structure, but also on the minerals in the muds on the floor of 

 the ocean. § Of the effect of this destructive action they say: "In all 

 cases, however, calcareous structures of all kinds are slowly removed 

 from the bottom of the ocean on the death of the organisms, unless rap- 

 idly covered up by the accumulating deposits, and in this way protected 

 to a certain extent from the solvent action of the sea water. It is evi- 

 dent from the Challenger investigations that whole classes of animals 

 with hard, calcareous shells and skeletons, renuiins of which one might 

 suppose would be preserved in modern deposits, are not there repre- 



^ Loc. cit., pj). 94-95. 

 tioc;. c«.,p. 100. 



i Report on the Scientific Results of the Voyage of H. M. S. ChuUenger. Deep-Sea 

 Deposits. 1891. p. 337. 

 § Loc. cit., p. 255. 



