136 
BULLETIN OF THE LABORATORIES 
the rock in all directions. The following measurements of the feli 
spar crystals were made: 
20°+23°=43° whole angle. 
35°+3o°=65° - 
25 ° + 23 °=: 48 ° 
According to Pumpelly’s method this would make the feldspar 
labradorite. The crystals are exceedingly regular in form, cutting 
each other in many directions. Inclusions in the crystals are frequent, 
presumably fragments of the magma. Colors of polarization gray, 
yellow and blue. Minute crystals of feldspar, all of about the same 
size, thickly dot the black magma. These are probably of the same kind 
as the larger crystals. 
The next ingredient which attracts attention is the augite. This 
is not nearly as abundant as the feldspar and does not occur in as large 
crystals. The form of the crystals is rarely regular, generally some- 
what rounded. Inclusions of minute needles of apatite are frequent 
in the augite, also a greenish alteration product, otherwise it is un- 
altered. 
No. 1083 (Plate XIII, Fig. 8.) is a weathered specimen of the 
same rock. The specific gravity is 2.66, being much lighter than the 
original rock. Here an excellent opportunity to study the effects of 
w^eathering is afforded. The augite has entirely disappeared, not a 
single crystal in the section possessing any of the augitic characteris- 
tics. A greenish product, much colored by the iron of the magma, 
probably represents the decomposed augite. The feldspar, while in 
many cases still retaining its crystalline form, is in every case altered, 
generally from the center. The figure shows one of the less altered 
crystals beginning to decay in the center. The alteration product is of 
a light green color, very irregular in form, but in a few cases the regular 
form of the primitive crystal is retained. The aphanitic magma of the 
unaltered rock has changed to a yellowish brown, with small crystals 
of magnetite dotting it all over. 
No. To82a (Plate XIII, Fig. 7.) is the next phase of the dia- 
base. It is a somewhat porphyritic diabase of much lighter color than 
any of the preceeding, being almost reddish-brown, and showing some- 
what the effects of weathering. The specific gravity is less also than 
any of the preceeding, being only 2.6. The fracture is somewhat 
conchoidal though not as much so as No. 1082. Under the micro- 
