34 The American GeoUxjist. July. 1895 
products wcro observed in a few sections. Although consid- 
erable plagioclase is present it is decidedly secondar}^ in 
amount to the colored silicates. The idioniorphic habit so evi- 
dent in the diabases lias disappeared, but the lath-shaped 
form and twinning are very easily recognized. Dikes Nos. 
12, 14, 19, 24, 27, 34 are augite camptonites. 
No. 12. Augite is the chief colored silicate in this dike. 
Two generations are present. The phenocrysts exhibit marked 
zonal structure, the centres being nearl}'^ colorless or light 
shades of yellow or green, and rims various shades of pink 
with slight pleochroism. In general, it may be said that 
the greater variation in color the stronger the pleochroism. 
The augite of the second generation is allotriomorphic with 
the same optical features as the porph3'ritic constituent and 
filling the interstices between the plagioclases. The horn- 
blende present is very small in amount. Only a few flakes 
and ragged blades were noted. The plagioclase, although 
quite subordinate, shows the usual twinning and bladed 
form. Olivine crystals and grains are not uncommon. Ser- 
pentine is more or less closely associated with the olivine. 
Magnetite is also quite abundant. 
No. 14 ditfers from No. 12 in containing more hornblende, 
but it is still secondary in amount to the augite. Only 
one generation of hornblende is i)resent and it is ag- 
gregated in bunches throughout the section. The individ- 
uals are idioniorphic and highly pleochroic, bright yellow- 
ish brown to deep brown. Cross-sections show the following 
forms: oo P, c»P^, ocPoo'. Augite in two generations forms 
the larger part of the rock. The phenocr3'sts are exception- 
ally well developed, showing excellent zonal structure in 
nearl}' every individual, the centers being light yellow or 
colorless and the rims bright yellow with slight pleochroism. 
In cross-section the following faces are easily recognized: 
a)P^, ooPoo', ocP. The followingangles were determined by 
means of the graduated stage : I a 1 = 88^ ; ii a 1=132°. Veiy 
little fresh olivine was recognized. The larger phenocrj'sts 
have passed into serpentine, the crystalline outline, however, 
being retained. The plagioclase is generally twinned and 
more abundant than in No. 12. The feldspar contains nu- 
merous inclusions of colorless needles with strong refractive 
