GEOLOGY. 217 



on which the bottom-temperature at like depths is 30, or even 

 lower. We have traced these two areas at corresponding depths 

 within about 20 miles of each other ; and where the bottom was 

 unequal, the slope of the plateau at the edge of the cold area, 

 or of a bank in its midst, raising its bottom out of the cold 

 stream into the warm which overlies it, a difference of 18.5 

 was found within eiylit miles. No contrast could well be more 

 striking than that which presented itself between the faunas of 

 these two areas. The Globigerina-mud was rigorously limited 

 to the warm; and of the animals living on its surface, a large 

 proportion were characteristic of the warmer temperate seas. 

 The bottom of the cold area consisted of sand and stones, and 

 of the animals which were abundantly distributed over it a large 

 proportion were essentially boreal. In the shallower portions of 

 the cold area, where an intermediate bottom-temperature pre- 

 vailed, an intermixture of the two faunae, corresponding with the 

 border position of this area between the temperate and boreal 

 provinces, was readily traceable. 



"Here, then, we have the remarkable fact that two deposits 

 may be taking place within a few miles of each other at the same 

 depth and in the same geological horizon (the area of one pene- 

 trating, so to speak, the area of the other), of which not only the 

 mineral character but the faunae are alike different; that differ- 

 ence being due on the one hand to the direction of the current 

 which has furnished their materials, and on the other to the tem- 

 perature of the water brought by that current. If the cold area 

 were to be raised above the surface, so that the deposit at present 

 in progress upon the bottom should become the subject of exami- 

 nation by some geologist of the future, he would find this to 

 consist of a sandstone formed by the disintegration of the older 

 rocks, the faunas of what would in a great degree bear a boreal 

 character ; whilst if a portion of the warm area were elevated at the 

 same time, the geologist would be perplexed by the stratigraphical 

 continuity with the preceding of a cretaceous formation, the produc- 

 tion of which entirely depends upon the extensive development of 

 the humblest forms of animal life under the influence of a higher 

 temperature, and which includes not only an extraordinary abun- 

 dance of sponges, but a great variety of other animal remains, 

 several of them belonging to the warmer temperate regions. He 

 would naturally suppose these widely different climatic conditions 

 to have prevailed at different periods, and would probably have 

 had recourse to the hypothesis of a "fault " to account for the 

 phenomenon. And yet these formations have been shown to be 

 going on together, at corresponding depths, over wide contiguous 

 areas of the sea-bottom, in virtue solely of the fact that one area 

 is traversed by an equatorial and the other by a polar current. 

 Further, in the midst of the land formed by the elevation of the 

 cold area, our geologist would find hills, some 1,800 feet high, 

 covered with sandstone continuous with that of the land from 

 which they rise, but rich in remains of animals belonging to a 

 more temperate province, and he might easily fall into a mistake 

 of supposing that two such different faunas occurring at different 



