﻿152 SMITH. 



In the first and last localities named it is found in fragments or blocks 

 indefinable from the schists, without any apparent connecttion with any 

 other similar igneous rock; however, at Caraon it is seen as a great 

 intrusive mass over a quarter of a mile in width, bordered on both sides 

 by well-defined schist zones. A very interesting thing about this in- 

 trusive mass is its various phases. I have traced this dike across the 

 country for a mile or so and have seen it grade from a quartz-feldspar- 

 muscovite rock into one of quartz and muscovite, quartz and feldspar with 

 no mica, and finally into a phase of pure quartz. The rock is quite white, 

 slightly greenish in the weathered portions, fairly coarse grained and it 

 possesses an uneven fracture. It consists of quartz, feldspar (plagio- 

 clase) and muscovite mica, although sometimes the micas when decom- 

 posed give the appearance of being biotite. There are also phases which 

 have a very granular appearance. 



Microscopic. — The rock is seen very largely to consist of quartz in 

 both large and minute irregular grains. Some feldspar, usually dirty 

 and cloudy, occurs, apparently plagioclose, as all that I made out to be 

 feldspar at all showed twinning of the albite order. I was able to find 

 symmetrical extinction in only one specimen and in this the angle found 

 was 10° to 12°, which would identify the mineral as an oligoclase. 

 Pericline combined with the albite twinning also occurs. 



No trace of micas remains in the slides which were examined, but 

 dirty-greenish aggregates of decomposition products only could be ob- 

 served ; under high power these were seen to be very minute, low, doubly- 

 refracting bodies, which may be zoisites and chlorites. I should judge 

 from the appearance of the slides that there had been a considerable 

 occurrence of deformative stresses throughout the entire mass from which 

 these samples came, as minute granulation is quite marked throughout 

 the slide. This deformation probably dates back to the time of the intru- 

 sion of the mass. 



Analysis. 4 



Per cent. 



Si0 2 72.56 



A1 2 : , 15.13 



Fe 2 0; 2.54 



MgO .95 



CaO 2.01 



Na 2 5.06 



K 2 .56 



H 2 O+110° .03+100 



H 2 0— 110° .93+110 



Ti0 2 Trace. 



P 2 5 None. 



MnO .46 



4 Analysis by Mr. L. A. Salinger, Chemical Division, Bureau of Science. 



