Shaler.] 126 [June 16, 



it. It has also quite a strong superficial resemblance to the common 

 Azelina Hiibneraria Guen., a geometer. 



Dr. T. M. Brewer exhibited a fine specimen of the Tringa 

 cornutus, a species formerly common on the N". E. coast, but 

 at present supposed to be of very rare occurrence. Mr. F. 

 L. Tileston had, however, found it on Cape Cod, about May 

 20, in abundance, and had kindly procured the specimen on 

 the table for the Society's collection. The thanks of the So- 

 ciety were voted to Mr. Tileston for the gift. 



The following paper was presented in substance at the 

 meeting of April 7, but received too late for insertion in the 



records of that meeting. 



• 



Propositions concerning the Motion of Continental 

 Glaciers. By Prof. N. S. Shaler. 



Ever since I have become convinced that the surface of North 

 America, north of the parallel of 40 p , was covered to a great depth 

 by a mass of ice during the last glacial period, I have been constantly 

 endeavoring to form a conception as to the nature of its movement. 

 This problem, which has doubtless led many naturalists into similar 

 difficulties, has, it seems to me, some light thrown upon it by the 

 considerations I shall summarize in this paper. It is evident that the 

 angle of declivity of the slopes over which the ice movement of the 

 glacial period extended cannot account for the motion. There is, for 

 instance, indubitable evidence that during the last glacial period the 

 country between Cincinnati, Ohio, and the Laurentian Mountains, 

 was deeply ice wrapped, and that at the same time we had a great 

 amount of material from the Canadian section transported to the 

 Ohio valley. 



We also have evidence that the ice sheet furrowed the surface as if 

 it had moved as a continuous, or tolerably continuous mass, and it has 

 therefore been assumed, it seems to me hastily, that the behavior of a 

 continental glacier must have been essentially the same as that of a 

 valley glacier, i. e., that it had a continuous movement from the inner- 

 most point to the border. 



In the following considerations I hope to make it evident that this 

 supposition of the continuous movement which should bring any par- 

 ticle of ice over a distance of say eight hundred miles from the Lau- 



