REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r91 



The black rocks show infrequent augen of dark color which are 

 usually bordered by a green cataclastic zone of shattered feld- 

 spar fragments. The dark silicates constitute from 40;^ to 50^ 

 of the rock. Bronzite is preponderant, augite and hornblende 

 are also present in considerable quantity, and a little biotite 

 appears, usually around magnetite, of which considerable is at 

 hand. No garnet appears, but apatite and zlreon are prominent, 

 and some little pyrite occurs also. The rock is very finely granu- 

 lar, with a few feldspar and quartz fragments of somewhat larger 

 size. There is nearly or quite 10^ of quartz, a large content for 

 so basic appearing a rock. 



About lOfo of the feldspar is plagioclase. In the half dozen 

 fragments properly cut the prevailing extinction angle measured 

 from the albite twinning plane is 10°, in one case however reach- 

 ing 17°. The mineral is probably andesine. The remainder of the 

 feldspar is of intergrowth types, mostly of the prevalent faint 

 microperthite. There is also present considerable of a micro- 

 graphic intergrowth of an unusual and striking type, identical 

 with that in the augen gneiss just described (no. 11). The rock 

 as a whole clearly is a basic phase of the syenite. It is consider- 

 ably more basic than the augen gneiss (no. 11) and would seem a 

 quite typical monzonite. 



The, most basic rock collected was obtained about J mile east 

 of the depot. It is a heavy, fine grained, black rock (no. 6) in 

 which no augen were noted. It contains 50^ of dark minerals, 

 abundant hypersthene (or bronzite), augite, hornblende and 

 magnetite, some biotite and a little garnet, this latter idiomor- 

 phic and not around the magnetite. As usual, there is consider- 

 able apatite, but zircon is not so' abundant as in most of the sye- ' 

 nite. Most of the biotite is primary apparently, though in part 

 it results from hornblende alteration. All of these minerals are 

 quite as in the preceding rocks, except that the orthorhombic 

 pyroxene is rather more strongly pleochroic and may. be hypers- 

 thene instead of bronzite. 



Quartz makes some ofc of the rock. It shows a tendency to the 

 flattened form, though not so pronouncedly as in the more acid 



