Gushing — Geology of Clinton County. 



541 



an altitude of about 1,000 feet. One mile southwest of Dannemora, at about 

 the same elevation, is a considerable accumulation of sand w ith streaks of 

 gravel, perched on the valley side about 400 feet above the river, and sand 

 at about the same level shows at several points between. Both here and in 

 the Ausable valley, these delta deposits of the old lake seem to run higher 

 than heretofore recognized. 



Black Brook. 



This is the largest township in the county, and lies in the southwestern 

 cornei", adjoining Franklin county on the west and Essex on the south. Its 

 western half is wild, and much of it is quite inaccessible. The valleys are 

 wide with few exposures, and the ridges are difficult of access, forest clad, 

 and with their northern slopes heavily drift covered. Hence it is extremely 

 difficult to find outcrops in sufficient number to permit of accurate mapping. 



Series F. With the exception of the extreme southwest, the entire 

 township is occupied by gneissic rocks which, for the present, must all be 

 classed together. There is comparatively little of the ordinary microperthitic 

 gneiss. Such is found on the northern border, and on Palmer hill at the 

 east. But even on Palmer hill and along the river at Ausable Forks there 

 is much microcline gneiss, and much of the gneiss contains abundant green 

 morioclinic pyroxene. This association of pyroxenic gneiss with the Palmer 

 hill magnetite deposits is of interest in view of the like association at Mine- 

 ville, as reported by Kemp.'"" The same also occurs at Lyon mountain. In 

 some of the Palmer hill gneisses there are titanite rims around the magnetites, 

 a curious circumstance considering their juxtaposition to the ore-bodies. 

 These gneisses are w ell show n along the railroad just east of Ausable Forks. 

 In these exposures is a sheared strip, three inches w ide, in a coarse pegmatitic 

 band, which consists wholly of slickensided chloritic material. Just east of 

 the Forks is a heavv band of basic gneiss, which is hard and firm, and 

 contains, in addition to hornblende, plagioclase, biotite and magnetite, much 

 hypersthene but no monoclinic pyroxene. It is the only rock of the kind 

 seen in the county. The peculiar microcline gneisses, which have been 

 described on a previous page, are widespread in the central part of the 

 township, and the ponderous east and west ridge known as Silver Lake 

 mountain, is wholly composed of them. 



At Union Falls, the river drops twenty feet over gneiss and passes north' 

 eastward in a gorge, exposing an excellent section in w hich the very v ariable 



* Report New York State Geologist for 1S93, Tart I., p. 44! 



