550 



Report of the State Geologist. 



Champlain clays and sands, but from thence westward to the hills everything 

 is concealed by the drift and sand. 



Series I. Three northeasterly trending gneissic ridges rise in the western * 

 third of the township. The most northerly of these is a narrow ridge know n 

 as Burnt hill, which rises rather abruptly from the Salmon river valley, but 

 whose summit is only a little above the level of a plain of Potsdam sandstone, 

 which overlaps it on the north. In the central-west is the wide, massive 

 ridge of Terry mountain, and to the south is a somewhat disconnected ridge 

 coming in from Black Brook, the most easterly summit of which is called 

 Mt. Etna. The larger part of the gneiss is of the ordinary microperthitic 

 variety. A quite prominent gneiss on Mt. Etna is a quartz plagioclase gneiss, 

 with some microcline and orthoclase, and with hornblende, biotite and magne- 



tite present in considerable amount, so that the rock is well foliated. The 

 Burnt hill gneiss contains much microcline, that mineral often constituting 

 more than fifty per cent, of the rock. 



Series II and III do not appear in the township. 



Series IV. Potsdam scwidstone. Though the Potsdam must occupy 

 much of the central part of the township, the exposures, with one exception, 

 are close to the gneiss, poor, and possess no special interest. At Lapham's 

 mills the Little Ausable is in a new channel, and about thirty feet of Potsdam 

 is there exposed, all rather coarse, some of it red, but mostly buff or brown 

 in color. The dip is to the southwest, and rocks of Calciferous age surround 

 it on all sides. That in the river bed at Peru, one mile to the southwest, has 

 the same dip, while the exposures to the north and east dip to the north- 

 east, and a, fault must lie between them and the Potsdam, this fault being 

 probabh along t he summit of a low fold. 



