Association of American Geologists and Naturalists. 137 



these shells, which had been dispersed by the drift, and thus lodged 

 in the Brooklyn hills. The number of species comprised in the col- 

 lection amounts to ten or twelve, among which are those now most 

 common to our shores. 



These discoveries in regard to the drift appear to agree with those 

 which Sir R. Murchison states to have been made in the drift of 

 Europe. They must be admitted as proving that the most common 

 species of our present molluscs were of prior origin to the hills where 

 the remains were found, and probably older than the entire forma- 

 tion of drift and boulders which is found in the northern states. 

 The species obtained are not such as indicate a colder climate than 

 now prevails. But the shells found by Professor Emmons and others 

 in the pleistocene clays on the borders of Lake Champlain, and by 

 Mr Lyell and others in Canada, appear to belong to a later period 

 of the drift; and Mr Ptedfield infers that they were brought in from 

 more northern regions, or from deeper waters, by the great arctic 

 currents which must have swept over those regions, during the drift 

 period, when this portion of the Continent was deeply submerged. 

 These polar currents, annually freighted with immense fields and 

 islands of floating ice, such as are now diverted along the shores and 

 banks of Newfoundland, till they are met by the dissolving influence 

 of the Gulf stream, nearly in the latitude of Boston and New York, 

 he considered to have been among the chief agents in producing the 

 remarkable phenomena of the drift period. 



M. Desor stated, that discoveries in Scandinavia and northern 

 Europe shewed that the two geological epochs were the same in this 

 country and Europe, that the first deposite of the drift, consisting of 

 coarse clay and gravel, and stratified, was of a turbulent character, 

 while the second was quiet. Boulders have been brought from the 

 northwest, striated and scratched all over their surfaces. How much 

 of the phenomena, presented upon a close survey of these drifts, was 

 attributable to currents of water, M. Desor would leave to others to 

 say. For his own part, he believed that these drifts gave evidence 

 of the action of a body different from water. If the drift and boul- 

 ders were connected in the action, he fully believed that some other 

 agent than water must be looked for to account for their existence. 

 He could not agree with Mr Redfield in the positions which he had 

 assumed. 



Mr Redfield was not disposed to look for foreign causes to ac- 

 count for geological phenomena when one of a more domestic char- 

 acter was entirely adequate to produce these phenomena. Two great 

 polar currents are constantly setting southward — one to the south-east 

 from Hudson's Bay, the other to the south-west from the shores of 

 Greenland — these two currents unite near the Gulf stream, and 

 result in ono current. These currents bring along immense masses 

 and islands of ice. These islands bear along rocks, pebbles, &c., 

 collected on tiiem before their separation from the land where they 



