370 BULLETIN OF THE 



current of the Atlantic is one of the greatest and most powerful of all 

 known currents. 



Another side of this subject is also immediately connected with 

 deep-sea soundings. Geologists, and especially those of the school of 

 Lyell, have again and again assumed the slow rising of extensive 

 tracts of land from beneath the water, and taken all sorts of loose ma- 

 terials irregularly scattered over the surface of the land as evidence of 

 its former submersion. But since the dredge has been applied to the 

 exploration of the deep, and a great variety of animals, in a profusion 

 rivalling that of shoal waters, have been brought up, not only from 

 the immediate vicinity of the land, but at various distances, in increas- 

 ing depth, from one to two and even many hundred fathoms, no ob- 

 server is justified in considering extensive deposits of loose materials 

 as marine in which no trace of marine organic remains are found. The 

 very mud and sand of the deep teem with innumerable microscopic 

 living beings, the solid parts of which are easily detected in the small- 

 est samples of marine deposits, and may therefore afford a satisfactory 

 test where larger animals or plants are wanting. Now, after surveying 

 the whole width of our AVestern prairies, without finding anywhere a 

 sign of marine animals or plants, I cannot see that there is any evidence 

 of their marine origin, or of the influence of oceanic currents in accu- 

 mulating or distributing the loose materials scattered over those vast 

 plains. On the other hand, I have ascertained that the foundation rock, 

 upon which these materials rest, is everywhere polished, grooved, and 

 scratched in the same characteristic manner as the well-known glaciated 

 surfaces, wherever exposed. I have seen such polished rocks in the 

 valley of the River Platte, not far from Omaha, and am now satisfied 

 that the whole extent of the country, between the Alleghanies and the 

 Rocky Mountains, was one unbroken glacier bottom. The scratched 

 pebbles found among the loose materials of the great prairies confirm 

 this view. For similar reasons, I am satisfied that the valley of the 

 Amazons has not been under the level of the ocean since the tertiary 

 period. 



The most perplexing feature disclosed to me by our deep-sea dredg- 

 ings and by my observations of the sea-shones along the Gulf Stream, 

 on the Florida and on the Cuba side, is the irregularity of the strati- 

 fication of the Spanish banks as compared with the deposits on the 

 American side. 



