286 AUSTIN F. ROGERS 
crystallization. Apparently the more abundant the aegirite is, the 
more abundant the albite. 
An interesting case of alteration was found in one of the veins. 
Specimens of a vein some distance apart were collected before they 
were discovered to be the same rock. One of these (No. 44) was a 
fresh rock, greenish-gray color, with abundant crystals and needles 
of aegirite. The other specimen (No. 23) was gray with a dead look. 
The aegirite had disappeared and abundant magnetite had formed 
at its expense. The outlines of the aegirite crystals were filled with 
magnetite dust, and there were many large magnetite grains and 
crystals all through the rock. 
RIEBECKITE PEGMATITE 
At the foot of Main Street, in the town of Granite, near the base of 
the mountain, a pegmatite vein six and one-half inches (16°™) wide 
was found. It occurs in the coarse granite and has a nearly east-west 
strike with dip toward the north. ‘The striking thing about this rock 
is the occurrence of prismatic crystals two or three centimeters long 
and $°™ in diameter. They have the six-sided cross-section of the 
amphiboles, and often appear with a central core of orthoclase. The 
other minerals are quartz, orthoclase and a little albite. The rock 
has the typical vein structure, for at the center is a band of fine-grained 
rock, on either side a zone of coarse-grained rock, and then on each 
side at the contact with the wall rock there is a band of fine-grained 
rock. Each of the bands is about 3°™ wide, but the vein is not 
quite symmetrical. 
DIABASE DIKE 
A short distance east by northeast of Mt. Walsh a fine-grained, 
black, basic dike, about four and one-half feet wide occurs. It has 
an east-west strike and almost vertical dip. The rock is exposed in a 
prospect shaft and is much altered. It consists of lath-shaped plagio- 
clases, amygdules filled with a chlorite-like mineral (representing 
original ferro-magnesian mineral), and abundant magnetite. The 
rock has the typical ophitic structure, and so is a diabase. 
An interesting thing about this dike is that it can be traced across 
the mountain by the character of the vegetation, though the rock is 
only exposed in one spot. ‘The vegetation on the mountain is very 
