MUSEUM OF COMPARATIVE ZOOLOGY. 19 



isolated peaks of those ranges. He divides the boulders which rest upon 

 the surface of the drift into two classes, according as they are rounded 

 or angular, those which make up the trains being rounded, while the 

 angular are distributed without definite arrangement. He considers 

 that the trains owe their formation to the movement of the general ice- 

 mass, which rested upon the region during tlie glacial period, the 

 boulders which are found in trains, and which he believes to be rounded, 

 having been torn from prominent peaks and forced along under the ice- 

 sheet, while the scattered and angular ones were transported to their 

 present position much later, when the ice-mass had become so reduced 

 in thickness that the peaks in question projected above the surface, so 

 that masses of rock could become lodged iipon the ice, as well as be 

 dragged beneath it. 



Since boulders arranged in distinct trains are somewhat exceptional, 

 it seems desirable that all the facts immediately connected with such 

 boulders should be made known as fully and accurately as possible. 

 With this end in view, a survey of the trains and other glacial phe- 

 nomena, together with the topographical and geological features of the 

 region was made by the writer, and the results of that survey have been 

 indicated, so far as possible, upon the larger map which accompanies 

 this paper. 



The account of the boulder trains themselves will be preceded by de- 

 scriptions of: 1. The Geography and Topography. 2. The Bed-Rocks 

 of the Region. 3. Glacial Markings upon the Bed-Rocks. 4. Super- 

 ficial Deposits underlying the Trains. 



I am indebted to the courtesy of Professor H. F. Walling for the 

 skeleton map of Richmond and surrounding towns, which I was enabled 

 by his aid to prepare before visiting the field of study. I take this op- 

 portunity to present to Mr. M. E. Wadsworth also my thanks for his 

 kind assistance in determining some of the rocks of the region, and espe- 

 cially for his study of the thin sections which were made. 



To Professor N. S. Shaler and Professor J. D. Whitney, I wish to 

 express my sincere gratitude, since I feel under great obligations to 

 them, not only for timely suggestions with regard to the preparation of 

 this paper, but for the many favors and the valuable instruction and 

 counsel which I have received from them in years past. 



