262 
Buell—Geology of the Waterloo Quartzite Area. 
gin of the ridge that borders the broad, marshy basin of the 
Crawfish river. Its linear extent is a quarter of a mile, and 
its breadth at center is thirty rods. As the rock also appears 
in a shallow well a quarter mile east of the ledge, it is proba¬ 
ble that a considerable area of thinly covered quartzite lies be¬ 
tween the exposed ledges and the high drift ridges to the west. 
The narrow ledge area of four or five acres evidently repre¬ 
sents a glacially abraded surface of at least thirty acres. 
The ledges forming the Mud Lake area were also located by 
tracing to their origin their trains of bowlder drift. In Pres. 
Chamberlin’s description of the area just referred to, mention 
was made of quartzite bowlders at a considerable distance to 
the north and east of the ledges which were then known. 
From information obtained from residents of the region I was 
led to the largest of these ledges at the beginning of my work. 
This exposure is on the west side of an isolated ridge that lies 
in the marsh basin north of Mud Lake. Its length is eighty 
rods and its greatest breadth about sixty rods. The ledge 
surface on its margins rises abruptly from the marsh, but its 
highest points do not exceed twelve feet above the general 
level. The rock surface is also exposed in the bed of the creek 
that flows through the marsh west of the ledge and indicates 
an indefinite extension of the outcrop beneath the peat accu¬ 
mulations of the marsh basin. The presence of quartzite bowlders 
in the glacial drift on the west side of this marsh and farther 
north than these exposures was observed at the time of the 
location of these ledges, but was first explained by supposing 
that concealed ledges exist in the marsh farther north than 
those already seen. But their frequent occurrence on the east 
side of this basin led to successful search for exposures on that 
side also. The eastern border of this bowlder train was followed 
from the vicinity of Hubbellton northward across Shields town¬ 
ship and the erratics were traced to their source in a small 
ledge on the east side of the marsh in the northeast corner of 
Section 2. This exposure consists of low swells of rock, the 
highest rising less than five feet above the marsh, and is in¬ 
cluded within an area of about four acres. The bowlder train 
traced to this point stops at the ledge surface, only a single 
