488 
Buell—Bowlder Trains. 
north and northeast of this region clearly shows that the 
former present specific differences, so well marked as to lead to 
their ready recognition in the area of their glacial distribution. 
EVIDENCES OP GLACIAL DISTRIBUTION. 
These may be briefly summarized as follows: 
1. Abrasion of the ledge surfaces. —These, wherever exposed, 
bear evidence of intense abrasive agencies. The highest out¬ 
crops present rounded, moutonnee forms and briefer exposures 
often show smooth tabular surfaces. The low reliefs of the 
larger ledges are also significant. The Mud Lake ledges have 
an elevation of but five and twelve feet, respectively, above the 
marsh level in areas of twenty and fifty rods breadth, and the 
largest ledges of the Portland group rise only from thirty to 
forty-five feet above the surrounding marsh. 
Glacial striations are everywhere present and agree in direc¬ 
tion with the lines of drift movement indicated by the accumu¬ 
lations of the latest glaciation. These vary from S.5°W. in 
the most remote ledge of the Mud Lake area to S.34°W. on 
the slopes of the western ledges of the Portland area. Com¬ 
parison of ledge profiles with those obtained from exposures of 
similar rock in the driftless areas indicates that many feet of 
rock have been removed from these surfaces by glacial action. 
2. Distribution of drift material. — The evidence upon this 
point is exhaustive and is comprised under the following heads: 
a. A greatly increased amount of bowlder material at all 
points favorable for observation in the line of glacial movements. 
The general facts of this distribution are indicated upon the 
map of the area, and the amount of this material is given in 
the descriptions of the bowlder trains. 
b. The recognition in this increased bowlder content of the 
quartzite rock exposed in the ledge surfaces of the adjacent 
areas. 
c. Evidence of the local origin of this drift material in the 
absence of the imprint of extended glacial abrasion. 
d. The recognition of the specific types of quartzite rock found 
in the different ledges in the local crystalline drift over the 
whole area of the so-called bowlder fan. 
