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 the 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 upon 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 valnable instruction and 
counsel which I have received from them in years past, 
