138 The American Geologist. September, moi. 
quently occur in these tonalytes as well as in the granites. 
I'he former is composed of lime-soda feldspar, quartz, horn- 
blende, biotite and a little orthoclase. Magnetite, apatite, zir- 
con, sphene (titanite) and garnets are present as accessory 
constituents, and more or less secondary epidote is almost al- 
ways found. 
The hornblende-dioryte is a common type throughout the 
area. It is a coarse-grained aggregate in .which striated feld- 
spar and black, compact hornblende can 1)e readily distinguished 
with the unaided eye. More or less quartz is usually present 
and not uncommonly a little accessory biotite. On a fresh sur- 
face the rock has a mottled appearance due to the w'hite feld- 
spar standing out against the dark hornblende. But when it 
has been much weathered the surface becomes much pitted on 
account of the removal of the plagioclase. When quartz forms 
one of the constituents the other minerals weather out and 
leave the former projecting, giving the rock a rough exterior 
which is highly characteristic of the quartz-dioryte. The 
abundance of blue quartz is a noticeable feature of this type. 
It is commonly in good sized grains ranging- from one-eighth 
to one-sixteenth of an inch (one and a half to three millimeters) 
in diameter. With an increase in the amount of biotite this 
rock passes over intO' tonalyte. 
The most al)undant rock type in the whole area is probably 
the noryte, with which the gabbro is closely associated. The 
constituents of the former rock that are readily distinguishable 
are a greenish black or reddish brown hypersthene, often with a 
bronzy, metallic luster, and fresh striated feldspar. In addi- 
tion a little secondary diallage is usually present. The noryte 
is a medium coarse-grained, granular rock, often with a 
crumbly appearance due to its loose texture. It varies in color 
from gray to almost black, but the light colored varieties are 
the more prevalent. A noticeable peculiarity of this type is the 
development of green hornblende along certain planes where 
there has probably been more or less stress. These green 
bands, which have a width of several millimeters, usually stand 
out conspicuously on a weathered surface. In this region the 
norytes are more abundant and important than the gabbros. 
They differ from most of the other types of the area in being 
as a rule remarkably fresh and unaltered. One specimen each 
