538 



Report of the State Geologist. 



Dike No. 6<i, from Upper Chateaugay lake, is a typical olivine diabase, 

 in which even the olivine is surprisingly fresh. The pyroxene is of 

 lilac color, with quite strong pleochroism, \x yellow, b and c lilac. Its 

 phenocrysts are full of inclusions and markedly zonal. In the ground-mass 

 is considerable brown hornblende and some biotite, so that the rock grades 

 toward the camptonites. 



St ries VI. The Chazy lake valley has some features which suggest a 

 fault valley, but the lake is held in place by heavy drift deposits at both ends. 

 There are also heavy drift deposits at the upper end of Upper Chateaugay 

 lake. Bradley pond is but a remnant of a somewhat larger body of w ater in 

 a wide valley where the drift is unusually heavy, and whose surface is strewn 

 with multitudinous loose blocks of Potsdam. Three miles north of the pond, 

 in Ellenburgh, a watershed is formed by an accumulation of hills of modified 

 drift, sand and gravel with surface blocks of Potsdam, which stretches across 

 the valley from side to side. 



Saranac. 



Series I. Except for the southeastern portion, known locally as 

 Hardscrabble, the entire township is occupied by the gneissic series. The 

 most accessible exposures are those found along the Saranac river, from 

 Saranac hollow westward, the most notable being the section in the gorge 

 below the High falls. Excellent and repeated exposures are also found 

 along True brook. The gneisses in the township are for the most part of the 

 ordinary red, microperthitic variety, with the usual variations in the amount 

 of ferro-magnesian silicates present, and also with the customary bands of 

 basic gneisses, both the hornblende gneisses and the gabbroie gneisses 

 occurring. Along the North Branch of the Saranac, from Petersburgh west- 

 ward to Cold brook, are microcline and plagioclase gneisses which closely 

 resemble those in Black Brook township already described. 



Just east of Bussia, north of the road, is a strip of brecciated gneiss, 

 like that described by Kemp from Hammondville and elsewhere in Essex 

 county," the gneiss being in angular fragments of varying size cemented 

 together by a mixture of chloritic and other decomposition products. The 

 breccia has no great lateral extent and is cut by dike No. 33. 



Along True brook, in Lot 35, just above the old mill dams, are scanty 

 exposures of the only rock at all resembling quartzite which has been seen 

 in the county. Unfortunately the exposures are isolated, no others having 



• Reporl Of New York State Geologist lor 1808, Vol. I., p. 45fi. 



