DEEP-gfiA DEPOSITS. 549 



tbe rivers and tends thus to fill itself up. He considers however that 

 the sediments of the rivers, instead of extending- over all the ocean 

 bottom, are deposited near the mouth, Strabo attributes to the move- 

 ment of the sea, to its respiration, as it was then called, the impossi- 

 bility for the sediment to extend a great distance from the shore. The 

 wave, says lie, expels all foreign bodies from its bosom, producing thus 

 a purification. On the other hand, the presence of deposits of shells 

 in tlie interior of continents had not remained unperceived, and this 

 important observation leads Strabo to say that ''the sea has, during 

 periods more or less long, covered, then left dry, by withdrawing itself, 

 a goodly portion of the continents."* 



This different point of view may give a notion of ancient deposits 

 of the sea, and couvsequently .serve to clear up the history of present 

 deposits. 



The origin of organized fossil bodies, thus vaguely seen by several 

 philosophers of antiquity, was fully confirmed in the fifteenth and six- 

 teenth centuries. By a flash of genius, Leonardo da Vinci saw the 

 present sediment of the seas in the shell layers of the Apennines in 

 which, as engineer, he was making excavations. Bernard Palissy, ou 

 his side, without knowledge of this conclusion, was himself led to it 

 through his observations in Saiutonge. Simple potter as he was, he 

 offered to prove against all tlie doctors of the Sorbonne that fossils 

 are the debris of organisms which have lived in the place where they are 

 found, "while the rocks were nothing but water and mud, which became 

 petrified after the water dried up." No one is ignorant how this resem- 

 blance has been since then clearly recognized and accepted in regard to 

 the series of strata which succeed each other in enormous thicknesses in 

 the interior of the continents. Thus for a long time we have been com- 

 pelled to admit that fossiliferous strata result from the sediment formed 

 in ancient epochs of the history of the globe, during which time the 

 sea covered vast regions which have now emerged. 



The deposits which we see to-day forming in the ocean are the con- 

 tinuation of those which.have accumulated there through the ages since 

 the epoch when tlie mass of water condensed upon our globe and sur- 

 rounded it with a liquid envelope. 



The rocks continually attacked by atmosj^heric agencies are reduced 

 little by little to small fragments. The chemical action of the air, the 

 physical part performed by the water, the physiological influence of 

 plants concur to produce their more or less complete disintegration. 

 Continents, upon the surface of which this work is going on every- 

 where, are thus covered with the debris of the rocks which running 

 water can easily take hold of. Whether such waters are rivulets, tor- 

 rents, streams, or rivers, they seize, carry ofl", and drift toward the 

 ocean the mineral particles. This hap])ens even with tlie most tena- 

 cious rocks, such as granite. This detritus is partially arrested in the 



* Work cited, p, 86. 



