EVOLUTIONAL GEOLOGY, 297 



C, from which we may gain some kind of idea of the amount of com- 

 pression it nno-ht produce on the yielding- interior of the crust. To 

 admit that these views are speculative will be to confess nothing, but 

 they certainly account for a good deal. They not only give us ocean 

 basins, but basins of the kind we want; that is, to use a crude com- 

 parison once made by the late Dr. Carpenter, basins of a tea-tray form, 

 having a somewhat flat floor and steeply sloping sides; they also help 

 to explain how it is that the value of gravity is greater over the ocean 

 than over the land. 



The ocean when lirst formed would consist of highly heated water, 

 and this, as is well known, is an energetic chemical leagent when 

 brought into contact with silicates like those which formed the primi- 

 tive crust. As a result of its action saline solutions and chemical 

 deposits would be formed; the latter, how^ever, would probably be of 

 no great thickness, for the time occupied by the ocean in cooling to a 

 temperature not far removed from the present would probably be 

 included within a few hiuidreds of years. 



THE STKATIFIED SERIES. 



The course of events now becomes somewhat obscure, but sooner or 

 later the familiar processes of denudation and the deposition started 

 into activity, and have continued acting uninterruptedly ever since. 

 The total maximum thickness of the sedimentary deposits, so far as I 

 can discover, appears to amount to no less than 50 miles, made up as 

 follows: 



Fuet. 



Kecent and Pleistocene 4,000 Man. 



Pliocene 5,000 Pithecanthropus. 



Miocene 9,000 



Oligocene 12,000 



Eocene 12,000 Eutheria. 



Cretaceous 14,000 



Jurassic 8,000 



Trias 13,000 :\ranunals. 



Permian 12,000 Reptiles. 



Carboniferous 24,000 Auiphil)ia. 



Devonian 22,000 Fish. 



Silurian 15,000 



Ordovician 17,000 



Cambrian 16,000 Invertebrata. 



Keevveena\,an 50,000 



Penokee 14,000 



Huronian 18,000 



Geologists, impressed with the tardy pace at which sediments appear 

 to be accumulating at the present day, could not contemplate this 

 colossal pile of strata without feeling that it spoke of an almost incon- 

 ceivably long lapse of time. They were led to compare its duration 



