Niles.] 330 [March 20, 



action of the atmosphere through frost materially assists in the work 

 in our climate, but its action is most marked upon the upper portions 

 of the slopes, while the waves and currents work in their zone below. 

 I might easily multiply the applications of this principle, but it is my 

 object to present the general law in accordance with which the topo- 

 graphical features of mountains may be classified, and not to follow 

 it into minute details. 



Mr* S. H. Scudder exhibited drawings of a fossil butterfly 

 from Florissant, Colorado, the first fossil specimen of this 

 group of insects yet found in America. He has given the 

 name Prodryas to the form. 1 



Dr. T. M. Brewer called the attention of the meeting to a 

 bird new to our fauna, viz., the Louisiana Tanager, a speci- 

 men of which was taken in Lynn, during the severe snow 

 storm of February, where it was undoubtedly carried by the 

 gale from its home. 



General Meeting. March 20, 1878. 



Vice-President Mr. S. H. Scudder in the chair. Forty-one 

 persons present. 



Mr. Scudder announced the death, on March 17th, of Dr. 

 Charles Pickering, a member of the Society since 1858, and 

 so well known from his connection with the Wilkes Explor- 

 ing Expedition and his works upon the Races of Men and 

 the Geographical Distribution of Plants. 



It was voted to request Mr. F. W. Putnam to prepare a 

 notice of Dr. Pickerino-'s life for the Proceedings. 



The following paper was read : — 



Upon the Relative Agency of Glaciers and Sub-Glacial 

 Streams in the Erosion of Valleys. By Prof. W. H. 



Niles. 



In some remarks 2 which I made at a meeting of this Society in 

 April, 1873, I stated that my observations among the glaciers of the 



1 TJ. S. Geol. and Geogr. Surv. Terr. Bull, iv, ii. 



2 Proceedings of the Boston Society of Natural History. Vol. xv, pp. 378-381. 





