Structural Features of the Exposures. 
268 
quartzite pebble of the Waterloo type being found among the 
hundreds of cords of bowlders observed on several square miles 
of surface which were explored north of this ledge. The posi¬ 
tion of this ledge at the northeast limit of the quartzite range 
gives it great prominence in the study of the bowlder trains. 
The area over which these erratics have been found, forms a 
sector of eighty degrees divergence from this center and includes 
within its limits all of the other areas and bowlder trains. 
The location of several of these ledges by means of their 
bowlder trains is instructive and suggests the question 
whether there are not still other quartzite outcrops within the 
area. Facts relating to the bowlder distribution indicate that 
such is the case. Their presence in the marsh basin north of 
the Mud Lake exposures has already been suggested, and seems 
very probable. Evidence of a similar character exists in the 
interval between the Portland and Hub bell ton areas. On the 
surface of a sharp drift ridge midway between these areas a 
large amount of fragmental quartzite is found which is distin¬ 
guishable by its peculiarities of color and texture from any 
hitherto observed in the outcrops examined. It is apparently 
the product of abrasion from some near but concealed ledge sur¬ 
face. The existence of a ledge somewhere beneath the drift 
ridge itself has an increased probability from the observation in 
a well section on the south end of this ridge, of quartzite beneath 
eighteen feet of drift and thirty-six feet of red shade. The con¬ 
cealment of these supposed ledges by glacial drift and marsh 
accumulations renders their exact location a difficult matter. 
Structural Features of the Exposures —Within the last few 
years extensive quarrying has been carried on at two of the 
ledges, which has very well exposed the bedding planes of the 
rock. On the broad fresh fracture surfaces thus developed this 
structure is almost as plainly seen as in unaltered sandstones 
so that not only the inclination of the layers but much of the 
conditions accompanying their original deposition is satisfac¬ 
torily made out. 
Conglomerate layers are of frequent occurrence in all of the 
marginal exposures of the Portland area. In the most southerly 
outcrops on Section 3, Waterloo township, the ledge is chiefly con- 
