40 
augite is in most cases completely altered ; and there is much 
viridite, epidote and iron oxide. This rock is undoubtedly a 
diabase, although I am unable to find a particle of recognizable 
augite or even hornblende, the viriditic alteration being complete 
in all the sections examined. 
The viridite is very abundant and is considered of undoubted 
augitic derivation, from its sharp straight and very angular 
outlines, which are so characteristic of the augites in this class 
of rocks. Minute epidotes are in some cases very abundant 
and impart to the rock a yellowish green stain. The section is 
traversed by veins of secondary quartz. 
Dike 37.— Very fine grained and compact; macroscopic 
pyrite; color, greenish. This is of finer grain than any of 
the preceding and so highly altered that none of its original 
constituents are now recognizable, excepting by pseudomorphs. 
The section shows only a fine, compact, fibrous or scaly ag- 
gregate of viridite, opacite, epidote, calcite and kaolin, with 
numerous grains of iron oxide. Although so highly altered, 
I have no hesitancy in referring this rock to the diabase group. 
SECOND SERIES. 
Dike 12.— Very fine grained and compact; no macroscopic 
constituents; color, dark greenish gray. Under the micro- 
scope it is seen to be highly altered, but with portions of augite 
still fresh and showing pleochroism. Iron oxide very greatly 
altered to a grayish amorphous product. Other alteration pro- 
ducts as in preceding: sections. 
Dike 11.—Differs from 12 only in being of slightly coarser 
texture and in having suffered more from alteration ; augites 
completely changed. 
Dike 10.— Fine grained and compact; porphyritic with small 
greenish feldspars. Plainly a diabase, although the feldspars 
