The Portland Type. 
267 
ficient abundance to give a slightly schistose appearance to 
fractured surfaces. Variations in structure appear in the chief 
exposures, gradations occurring in the different layers from 
finely granular structure to conglomerates containing 
pebbles two inches in diameter. Its range in color is 
from light gray to drab in some of the finer textured layers, 
and to a blue or purplish cast in the ledges farthest east. 
Less variation is seen in its composition on microscopic ex¬ 
amination. Quartz appears in fragments of irregular form and 
varying size, from one millimeter downward to the limit of 
determination. The most common arrangement of the larger grains 
is in clusters which give rise apparently to the mottled appear¬ 
ance of the surface. The separate grains in these clusters often 
show extinction at nearly the same angle, and this with the close 
interlocking of such forms indicates that these groups are the 
fragments in situ of large individual crystals. Quartz and 
iron oxide, apparently magnetite, are mingled with the 
interstitial sericite which usually appears in flakes between the 
quartz areas. The usual inclusions in quartz are present, and 
in some sections indications of the alteration of the iron oxide 
to the hydrated form are noticable. This type of structure is 
shown in Plate VIII, Fig. 1 and Plate IX. Fig. 1. In the dis¬ 
tinctively conglomeratic layers the pebbles contain very little 
interstitial quartz material, but the matrix is in large part 
composed of inwrapping plates of sericite. 
The Hubbellton Type —Quartzites exposed in the ledges of this 
area have a quite different aspect and structure from the Port¬ 
land quartzites. They are homogeneous in texture, of blue and 
purplish tones, translucent and exceedingly brittle. Bedding- 
planes are indicated on the cross fracture by narrow bands of 
varying color and translucency. The outcrops at the north 
end of the area show dark bluish, somewhat banded layers, 
while those on Sec. 2, Waterloo township, are of a very brittle 
translucent rock of reddish purple color. The microscopic 
structure is similar in all the sections examined from these 
ledges. The larger quartz grains are commonly of elongated 
forms and exhibit a parallelism in arrangement. Their outlines 
are exceedingly irregular and they are usually bordered by 
