Cushing — Geology of Clinton County. 



539 



been noted within half a mile to the east, while westward from this point the 

 valley expands, and all rocks are heavily buried in drift. Grneissic ridges are 

 within a mile both to the north and the south, but the rocks accompanying 

 the quartzites in the valley are nowhere exposed. Megascopically, much of 

 the rock is white and granular, with occasional small red garnets showing, 

 and, but for the latter, looking quite like some parts of the Potsdam. Other 

 portions are coarser, showing both quartz and orthoclase, the latter predom- 

 inating, and with an arrangement of the quartz in leaves, resembling, in that 

 respect, the Canadian rocks which Dr. Adams calls " leaf gneisses."* 



Under the microscope, the rock is seen to be mainly composed of 

 microcline and quartz, with some orthoclase, a little plagioclase, and occa- 



sional garnets, the whole with a rather finely granular structure. A few 

 larger individuals give the impression that the rock has been granulated, 

 but it is not certain. In one of the two slides made, are found occasional 

 individuals of a nearly colorless mineral, whose parallel extinction, lii^'h 

 interference colors, small axial angle, and positive character are indicative 

 of sillimanite, though it is irregularly bounded and somewhat broken and 

 crushed. Its presence is of interest, as the mineral is quite characteristic 

 of certain schists closely associated with the limestones, and may perhaps 

 indicate the presence of the limestone series here concealed by the drift in 

 the valley. 



♦American Journal of Science, Vol. L., p. 62. 



