DEEP-SEA DEPOSITS. 565 



margiual deposits in extent. The great predominance of red clay and 

 globigerina-mnd ooze is noticed at first sight botli in the Atlantic and 

 in the Pacific. In regard to the diatom ooze, it is seen to abound in 

 the Antarctic Ocean beyond 50 degrees of latitude. 



The deposits in the abyssal regions are in complete contrast not only 

 with the present deposits of seas less deep, but also in a marked way 

 with those formed in the seas in ancient geological periods and which, 

 laid down for a depth of thousands of meters, constitute the series of 

 stratified rocks. 



In these ancient formations the sediments of abyssal nature seem to 

 be lacking, or to be at least very rare. Hence the conclusion that the 

 parts of the sea where sedimentary earths are successively formed are 

 not, as to conditions of depth, comparable to those where the abyssal 

 regions of the Atlantic and Pacific are found. They were not very far 

 from the emerged portions or continents, and did not attain to very 

 great depths. 



We are therefore led to the conclusion that from the most remote 

 epochs the continental elevations have occupied very nearly the same 

 parts of the globe. The prominences have been gradually modified by 

 general ujjheavals, as has happened on a small scale, for example, in the 

 formation of the Alpine chain. The great depressions then go back to 

 a great antiquity and the general configuration of the terrestrial sphe- 

 roid, with its vast and deei) depressions as we now know them, must have 

 been outlined from the most ancient epochs of its history. 



This is the confirmation of an idea which has been previously reached 

 from other considerations Agassiz formulated it in 1872, in discuss- 

 ing the observations made by Pourtales upon the deeps of the Atlantic, 

 and in remarking that no vestiges of stratified earth, either ancient or 

 modern, were to be found there. 



Various facts lead us to think that the clay which covers the bottom 

 of the oceanic basins was deposited with extreme slowness. The 

 deposit seems not to have been thick and seems to go back, at least 

 in certain parts, to very remote periods. This explains the relative 

 abundance with which the cosmic dusts, as well as the more enduring 

 of the cetaceous remains, are found there. The terrigenous deposits 

 accumulate upon an entirely different scale of rapidity. 



^ow that we know the mode of formation of the deposits in the great 

 deeps of the sea, and the chemical reactions producing the various 

 species of minerals, new horizons are opened to us with regard to phe- 

 nomena of which we formerly had no idea, and which nevertheless has 

 for its stage more than half the solid crust of our planet. 



The examination of the beautiful work under our notice shows how 

 numerous are the facts upon which the conclusions of the authors are 

 based. It proves also the conscientious care which was bestowed upon 

 the specimens procured which were examined by all themethods known 

 to science. 



