REPORT OF THE DIRECTOR 1916 2J 



Locally many variations in direction of strike occur, and there 

 is especially manifest a tendency on the part of the sediments to 

 wrap around the ends of the sills of igneous rocks. 



The igneous rocks of the quadrangle consist of gabbro and of 

 two different granites. The gabbro is much older than one of the 

 granites and is probably older than either, though its time relation 

 to the older of the granites can not be definitely ascertained. It is 

 everywhere highly metamorphosed and converted into the horn- 

 blende-feldspar rock called amphibolite for convenience. In its 

 marginal phases it is always a thoroughly foliated hornblende 

 gneiss or schist and can not be distinguished from similar gneisses 

 which are interbanded with the Grenville sediments and form a 

 characteristic constituent of that series. But in the larger masses 

 more solid, less metamorphosed cores are always present whose 

 igneous origin is clearly apparent. In the southeast half of the 

 quadrangle there was originally a large mass of this gabbro but it 

 has been badly cut up and cut out by the later of the two granites, 

 and now occurs in a number of disconnected masses. 



Of all the rocks of the quadrangle this gabbro was the most 

 susceptible to attack by the granite. Its marginal portions are 

 always full of masses of pegmatite and of quartz either as dikes 

 or as lenticles; and in addition there has also been much minute 

 penetration and soaking of the gabbro by the granite. Wherever 

 the two rocks adjoin there is apt to be a gradual passage from the 

 one rock into the other, no sharp boundary separating them can 

 be drawn, and to discriminate between granite-cut gabbro and 

 granite with plentiful gabbro inclusions is no easy matter. More 

 rarely, however, the boundary is quite sharp. 



The gabbro occurs in part in more or less oval masses which 

 plainly either wedge aside or else cut out the sediments and whose 

 intrusive nature is therefore clear; and in part in long, narrow 

 bands which probably represent sills and whose intrusive nature 

 is much more difficult to demonstrate. The long, narrow belt of 

 gabbro which lies just east of Moss ridge and whose prolongation 

 is associated with the rusty gneiss of the Stella pyrite mine at Her- 

 mon, is mostly thoroughly gneissoid and the proof of its igneous 

 nature is very difficult to obtain, though rather massive rock may be 

 obtained from within it at various places. Smyth shows a disposi- 

 tion to regard it as an igneous rock at the Stella mine occurrence, 

 and my study of the whole belt leads me to the same conclusion, 



