1870.] 75 [Pickering. 



above and from the north ; that thus the ice at one time in the basin 

 must slowly pass over the southern shore, as it gradually gave way 

 to the irresistible vis a tergo incessantly at work on the northern shore 

 of the lake. With a caution against the indiscriminate application 

 to ice of the conditions peculiar to the motion of water, he would 

 illustrate the matter by a familiar instance. Water passes from Lake 

 Superior into Lake Huron, and yet the bottom of the former is far 

 lower than either the surface or the bottom of the latter. If there 

 be no valid objection to this statement, he failed to see any reasonable 

 difficulty in the supposition that ice, during the glacial period, passed 

 from the basin of the great lake southward toward the Gulf of Mex- 

 ico ; indeed, some of the very channels which it probably eroded are 

 visible to-day. 



Dr. Charles Pickering said he found it difficult to adopt the view 

 of Dr. Jackson, as it supposed the boulders to have been brought 

 from a great distance. In the localities most familiar to him, he had 

 found the boulders not far removed from their original position — a few 

 miles only. 



He thought land and water might be so distributed as to make an 

 equal temperature on the surface of the globe. New Zealand is in a 

 somewhat high latitude, yet produces tree ferns . At Cape Horn it is 

 difficult to determine whether the climate is perpetual summer or 

 perpetual winter; snow falls at intervals throughout the year, but 

 quickly disappears, leaving the country always green; vegetation con- 

 tinues uninterrupted, and the natives go without clothing. 



Great geographical changes have taken place since the earlier 

 geological periods, for the crest of the Andes was once the bottom 

 of the ocean. 



Section of Entomology. December 28, 1870. 



Mr. J. H. Emerton in the chair. Nine members present. 



Mr. Edward Burgess exhibited a drawing of peculiar cu- 

 taneous muscles intersecting the nerve centre of the larva of 

 Darapsa myron, and crossing just before the third thoracic 

 ganglion, and causing an expansion or spreading of the gan- 



