22 NI-:\\' \()\iK STATE MUSEUM 



a contact mineral. Its occurrence in the pegmatites, however, sug- 

 gests caution in ascribing it all to such a source. 



The granite is chiefly found thoroughly interbanded with the 

 schists, injected into them parallel with their foliation, forming 

 apparent beds of hard, white gneiss which alternate with those 

 of schist. The beds vary in thickness from a few feet to many. 

 It is only in exceptional cases that the granite can be seen to cut 

 across the schist foliation. It is quite otherwise with the peg- 

 matite dikes from the granite which cut it and the schists in all 

 directions, and seldom follow the foliation. In the three small 

 areas which we have mapped as granite, the rock is full of schist, 

 ranging from mere films to bands many feet thick. These are 

 all thought to be stretched inclusions, though it is seldom possible 

 to demonstrate this. The bordering areas mapped as schist are 

 likewise full of granite and pegmatite dikes, so that the mapping is 

 highly conventional and merely roughly distinguishes^areas in which 

 granite is in excess from those in wdiich the schist predominates. 

 But the relations are much less simple and obvious than in the 

 Thousand Islands region where what we regard as similar relations 

 between Grenville and granite obtain. In passing across the 

 Adirondacks from west to east the Precambric rocks show a steady 

 increase in complexity because of ever more severe metamorphism, 

 until eventually, in the extreme east, the whole series has been so 

 enormously compressed and stretched that it is no longer easy to 

 recognize inclusions of sediments in igneous rocks, or dikes of 

 igneous rocks in sediments, owing to the apparent interbanding. 



There has also been much intermediate rock produced by a 

 thorough interpenetration of the schist by the granite. The exposed 

 granite masses are small, and we have not noted the evidence of 

 the actual digestion of schist by granite, with production of rock 

 of intermediate character, such as may be seen in the cases of the 

 larger batholiths of Laurentian granite. There has been much 

 injection of schist by granite, however, both along the foliation 

 planes with production of injection gneiss, and also of the mosaic 

 type in which the granite minutely penetrates the schist everywhere. 

 In many bands of this type an enormous amount of garnet has 

 developed. 



The pegmatites. It was the abundant dikes of white granite 

 pegmatite that first suggested the igneous nature of the white gneiss 

 and furnishes the chief evidence for it, aside from the chemical 

 composition. They cut through the granite everywhere and also 



