Notes on Some Rocks and Minerals — Emerson. loi 
constituents, magnetite abundant in angular crystalline 
groups, plagioclase with extinction 20 degrees for the smaller 
25 degrees for the much larger of the minute acicular crys- 
tals, the whole with complete ophitic structure. The glass 
basis is present in small portions, either in grotesque rami- 
fications in the larger feldspars, at times arranged in a beaded 
layer parallel to their boundaries or in isolated blebs. It is 
here often only partially devitrified but where it is wedged in 
the interstices of the very fresh crystalline constituents it is 
a reddish-grey granular mass showing aggregate polariza- 
tion. 
Diabase. — This rock is a crumbling pseudo amygdal- 
oidal mass much decomposed and carrying calcareous and 
chloritic amydules. It is considerably coarser than the 
preceding variety but the constituents can not be distin- 
guished without a lens. Under the microscope it has the 
aspect of a common diabase. The feldspar is abundant but 
wholly decomposed. In the freshest portion the augite is 
very little changed. Many large irregular cavities are filled 
with a red-brown radiated, fibrous mass of altered delessite 
showing a black cross when rotated under the nicols. These 
two rocks may very probably belong to a single series of 
dykes or have been derived from the border and center of 
a single large stock. 
Pickryie. — The third mass is fine-grained, greenish- 
black and fresh in appearance, and in it one detects with a 
lens scales of red mica and very rarely a triclinic feldspar. 
Microscopically it proved to be an unusually fresh and very 
interesting pickryte — an olivine-diallage-augite rock with 
some accessory plagioclase, which latter was wholly wanting 
in several slides, in others reached an amount which tempted 
one to associate the rock rather with the gabbros, which it 
resembles in texture. Tlie olivine which makes up certain- 
ly three-fourths of the mass, is often present in large and 
well formed crystals, and in smaller crystals crowds the 
other constituents. It is often quite fresh, often much 
decomposed and where the change is well advanced after the 
formation of the usual broad bands of yellowish serpentine, 
it turned in a new direction and the rest of the crystal has 
gone over into a mass of ])lumose scales which polarize in 
