12 NEW YORK STATE MUSEUM 



ville and the syenite. The more resistant syenite here forms a 

 high, steep rock-wall on the south side of the river, while the 

 less resistant Grenville gneisses have been deeply trenched by 

 the river [see pi. 2]. Moose river really bears about n, 40° e. 

 here and parallel to the foliation instead of nearly east and west 

 as shown on the map. 



In the area east of Fowlersville the Grenville rocks are chiefly 

 pyroxene gneisses. The gneissic structure is highly developed 

 and accentuated by the alternations of light and dark colored 

 bands although none of the rocks are very dark colored. The 

 bands are seldom more than a few inches thick. Microscopic 

 investigation shows the common rock to be made up as follows : 

 40 to 50^ of quartz; 25 to 30^ of large, bright green, pyroxene 

 crystals, sometimes slightly pleochroic; about 2^i of feldspar, 

 mostly orthoclase together with a little acid plagioclase ; 3 to 5^ 

 each of hypersthene and enstatite; and a little bronzite and 

 white pyroxene. Judging by the composition the sediments 

 from which these rocks were derived were probably shales or 

 shaly sandstones possibl;/ somewhat calcareous. These gneisses 

 are very similar to those referred to by Smyth as being directly 

 associated with limestone. Although no limestone is here seen 

 in outcrop, it is possible that some does occur along the east 

 side of the area which may thus account for the distinct depres- 

 sion (now drift-filled) along that side and from which some 

 softer or less resistant material has certainly been removed by 

 erosion. Associated with these gneisses are a few layers rich 

 in basic plagioclase feldspar and poor in pyroxenes and which 

 have the appearance of igneous rocks. This Grenville area forms a 

 long, narrow ridge which stands out as a distinct topographic feature. 

 Moose river has cut a channel across this ridge. The rocks dip at 

 an angle of 40° or 50° westward and strike almost due north and 

 south. Outcrops of syenite have been found on all sides of, and 

 pretty close to the Grenville mass. There are no sharp contacts 

 visible but it seems certain that we are here dealing with a long, 

 narrow inclusion of the Grenville in the syenite. This matter will be 

 further discussed below under the heading " Syenite gneiss." 



Syenite gneiss 



As indicated on the geologic map, syenite gneiss makes up a 

 considerable portion of the known Precambric area. From the 

 standpoint of both composition and structure it is very uniform 



