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Association of American Geologists and Naturalists. 271 



and Susquehanna, the communication by the valley of the Mississippi 

 becoming closed." At this stage of partial conversion to dry land, both 

 Prof. Mather and Mr. Hall conceive, if I do not mistake their views, 

 that the tertiary clays of Lake Champlain and the adjoining valleys 

 were deposited. Mr. Hall, adverting to the position of the post pleiocene 

 clays of Lake Champlain in relation to the drift, believes that " the facts 

 clearly establish distinct and widely distant periods between the forma- 

 tion of the great body of the drift in western New York and the erratic 

 blocks or bowlders," and he conceives " that the scouring and polishing 

 of the rocks has taken place at a period long anterior to the transpor- 

 tation of these northern bowlders, and that their passage over the sur- 

 face has had little or no connection with this phenomenon. 



Very similar views as to the physical condition of the region now 

 covered with drift, appear to be entertained by Prof. Mather. De- 

 scribing the phenomena throughout an extensive area, and assuming 

 about the same amount of submergence, this geologist has entered into 

 an elaborate and ingenious enquiry respecting the character and direc- 

 tion of the great systematic currents which should prevail under the 

 supposed distribution of land and ocean. Conceiving that the configu- 

 ration of the continent at the drift period was in the main the same as 

 at present, he shows that the great polar or Labrador current and the 

 Gulf Stream being the results of this configuration and the laws of 

 aqueous motion, connected with the rotation of the earth, and its belts 

 °f different temperatures, these currents must have existed then equally 

 88 a t the present day. The Labrador or polar current possessing ne- 

 cessarily a westward travel, he supposes to have flowed over the north- 

 em parts of the United States, bringing ice loaded with detritus. The 

 Gl *lf Stream, deriving from the rotation of the earth an eastward ten- 

 den cy, he supposes to have been parted by the mountain chain then 

 Wing the form of a great peninsula or island, and one portion to have 

 flo *ed up the wide plain or valley of the Mississippi, melting by its 

 warmth the ice of the Labrador stream, and causing its freights of 

 ro <% matter to be deposited over the country north of the Ohio and 

 Missouri rivers. The tendency of the southern current to set east- 

 Wa rd would, Prof. Mather thinks, convert the westward direction 

 of th e ice-bearing current into a southeasterly one, and he thus 



plains the southeasterly course which the detritus has evidently 

 taken. 



P fo f. Emmons, in his view of the condition which attended the dis- 

 persion of the drift, conceives that the first detrital stratum and the 



