GEOLOGY OF THE SCHROON LAKE QUADRANGLE 59 



flow-lines clearly preserved. Further, these well- foliated zones bear 

 a distinct resemblance to the gneissoid or amphibolitic border facias 

 of the gabbro already described, and thus we have here evidence 

 strongly supporting the view that the foliation of the amphibolitic 

 border facies of the gabbro is really essentially the result of mag- 

 matic flowage. 



The northern part of the small stock near the southern end of 

 Ledge hill is typical gabbro cut by one small pegmatite dike and 

 several small aplite dikes. 



Two small masses, one on Cobble hill and the other three-fourths 

 of a mile northwest of Loch MuUer are hornblende gneiss (meta- 

 gabbro?) quite certainly older than the granite. 



Aplite and Pegmatite Dikes 



Aplite. Aplite dikes w^ere observed in only a few localities 

 but probably others occur within the quadrangle. These are repre- 

 sented only in a general way on the geologic map. They probably 

 do not all belong to the same period of intrusion. 



The best display of aplite dikes is on Wilson mountain. These 

 are all medium to fine grained and none are foliated, neither do 

 they show any notable difference in coarseness of grain between 

 center and sides. On the western summit of the mountain a num- 

 ber of small aplite dikes, none over a foot wide, cut clearly 

 gneissoid, coarse-grained, pinkish granite. These do not have very 

 sharp boundaries against the granite. This fact, together with 

 their uniform medium-grained texture, suggests that these aplite 

 dikes were intruded under fairly deep-seated conditions not long 

 after the intrusion of the granite, or at least before the granite 

 cooled very much, so that the aplite magma was able to blend with 

 the walls of the granite country rock. 



On the eastern summit of Wilson mountain, numerous aplite 

 dikes very similar to those just described, and with a maximum 

 width of 4 feet, cut gneissoid medium-grained granite also without 

 very sharp contacts. 



The small mass of anorthosite and granite mixed rocks on 

 Wilson mountain (see map) is cut by a number of medium-grained 

 aplite dikes, the widest being 5 inches, and all showing rather 

 sharp contacts against the granite. 



Another locality is near the southern end of Ledge hill where 

 several aplite dikes very sharply cut the small gabbro stock. The 



