GEOLOGY OF THE SCHROON LAKE QUADRANGLE 



57 



a gneissoid structure is clearly evident. Much of this rock well 

 exhibits the peculiar mottled appearance so often seen in those 

 Adirondack gabbros which are relatively free from diabasic texture 

 and foliation, this mottling being due to the irregular distribution 

 of black minerals through the more or less granulated mass of 

 feldspar. No. 39 of table 4 gives the mineral content of a thin 

 section. This is a distinctly acidic facies and, like the local acidic 

 facies of the Texas ridge gabbro above described, may have resulted 

 from assimilation of granitic material by the gabbro. 



The small gabbro stock on the hill one-half of a mile west of 

 Irishtown contains a lo-foot inclusion of thin-bedded Grenville 

 quartzite. 



Fig. 4 A small exposure showing three facies of gabbro at the eastern 

 margin of the Oliver hill stock. The gabbro is cut by aplite and pegmatite 



dikes. 



Some interesting features were observed in connection with the 

 Oliver hill gabbro stock. Just south of the summit of the hill the 

 gabbro sends three dikes into the granite. None of these dikes 

 is more than a few rods wide, and one is amphibolitic. At the 

 extreme eastern end of the stock a small outcrop shows three facies 

 of gabbro one nonfoliated, another highly foliated, and a third 



