﻿GEOLOGY OF THOUSAND ISLANDS REGION 49 



Small titanites abound in the rock, magnetite and hematite appear in 

 varying quantity, with pyrite, apatite and zircon as other acces- 

 sories. 



Quartz is present in many of the bands but seldom in any great 

 quantity and often wholly absent. The feldspar is in part micro- 

 cline and in part plagioelase (andesine-labradorite) ; some micro- 

 perthite is usually found also, and often much feldspar not char- 

 acteristically marked. 



In addition to the above minerals the rock nearly always con- 

 tains calcite, and this in steadily increasing quantity as the dis- 

 tance from the granite bathylith increases. The rocks from the 

 schist inlier in the Potsdam due east from Omar, average 20 to 

 25^ of calcite; in the long ridge just to the north of this it occurs 

 in large, though somewhat less amount; while in the ridge north- 

 west of this, and nearest the granite, much of the rock shows but 

 little calcite, only the coarser, mottled beds having it in quantity. 

 The calcite is coarsely crystalline, in sharply bounded individuals, 

 and clearly formed at the same time as the other constituents of 

 the rock. 



The mineralogy of the schists strongly suggests contact effects, 

 the tourmalin, actinolite and epidote being especially suggestive in 

 this respect, none of them being normal Grenville minerals, away 

 from the immediate vicinity of igneous rocks. The green pyrox- 

 ene also is an abundantly formed contact mineral in the Grenville, 

 though not so distinctive of contact metamorphism as the others.. 

 These, with the constant presence of calcite, give an impression 

 that we are here dealing with a limestone belt much changed by 

 contact action, with the granite and pegmatite dikes which abund- 

 antly penetrate the series as the source of the mineralizing fluids. 

 The fact that these green schists, though here present in great 

 bulk, are not a usual member of the Grenville succession in the 

 general region, also suggests a local cause for their presence. It 

 would seem that a series so thick could not but occur repeatedly 

 elsewhere were it an ordinary member of the general series. Sim- 

 ilar rocks do occur in small bulk in the general schist series north 

 of Millsite lake, but their small amount here but emphasizes the 

 bulk of the other occurrence, 



As opposed to this suggestion of contact origin, the breadth of 

 the bejt and the distance it extends from the granite margin, 

 its general uniformity of character, whether in contact with a dike 

 or at a considerable distance from one, whether near the 

 granite margin or remote from it, (the only observed difference 



