6 The jhnerican Geologist. juiy, isai 
grains of microcline, zircon. The more common minerals are 
graphite, pyrite, albile, microscopic rutile and tourmaline; rarely 
galena and zinc blende. Thickness GOO-700 feet. This horizon 
was entirel}^ overlooked by Emmons, as his section happened to 
cross the mountain where this upper limestone is covered with drift. 
It belongs in his Lower Taconic No. 3, and in Walcott's Hud.son 
River as do the Greylock Schists. 
The Berkshire Schists (so named from their prevalence through- 
out Berkshire county): In character like the Greylock schists, 
but more frequently calcareous especially towards the underljMng 
limestone. Thickness 1000 to 2000 feet. Also forming a part 
of Emmons' Pre-Cambrian or Lower Taconic No. 3, "Talcose 
Slate," and Mather's, Hall's, and Walcott's Hudson River (Lower 
Silurian). Considerable allowance should be made for thickening 
in consequence of plications in the estimates of the thickness of 
both the Berkshire schists and the Greylock schists. 
The Stockhridge Limestone. Limestone crystalline, in places a 
dolomite, quartzose or micaceous, more rarely feldspathic. Very 
rarely f osilif erous. Galena and zinc blende rare. Irregular masses 
of iron ore (limonite) associated sometimes with manganese ore 
(p3'solusite) and with siderite, occasionally replaced to a small 
ey.tent by quartzite. Thickness 1200 to 1400 feet. Emmons' 
Pre-Cambrian Lower Taconic No. 2, (Stockbridge Limestone), 
Dana's Lower Silurian, Walcott's Trenton Calciferous and 
Chazy (Lower Silurian). From Mr. Foerste's and Mr. Woltf's re- 
cent discoveries in Vermont some of the lower part of this 
horizon may be Cambrian.* 
Tlie Vermont Formation. Quartzite, cropping out in the Gre}-- 
lock area only once (See Section G.) but possibl}* underlying the 
entire mass. Thickness 870 feet. Emmons' Pre-Cambrian, 
Lower Taconic, I. Granular quartz, Dana's Cambrian, Walcott's, 
in part Lower Cambrian, "Olenellus. " 
It should be noted that the maximum thickness estimated does 
not exceed the thickness usually attributed to the Lower Silurian 
in the Appalachian region. 
Areal Geology. The geological map of Greylock and the ad- 
jacent masses presents a great bod^- of the schists of the horizon 
of the Berkshire schists almost surrounded by the underlying 
*J. Elliot Wolflf, on the Lower Cambrian Age of the Stockbridge lime- 
stone, Bulletin of the Geological Society of America, Vol II. 1891. 
