382 
GEOLOGY OF THE FIRST DISTRICT. 
Rensselaer County. 
The rocks of the Hudson-river group, interstratified with other members of the Champlain 
division, occupy all of the county of Rensselaer, except the eastern parts of Hoosick, Peters- 
burgh, Berlin and Stephentown, which are occupied by the Taconic rocks. The quaternary 
deposits conceal the rocks over a large portion of the western part of the county ; but they 
are exposed to view in a multitude of localities along the banks of the Hudson and its tributary 
streams, in the hills, along the roads, and along the route of the railroad between the landing at 
Greenbush and the south line of Nassau. The most-singular contortions are seen in many 
localities along the line of this railroad. They are not more numerous or remarkable than 
hundreds of localities that might be named, but they are on a great line of travel, and may be 
examined by every one who passes. 
A mountain called Petersburgh mountain and West mountain, composed mostly of the rocks 
of this group, extends from between Stephentown and Nassau, through Berlin, the east part 
of Grafton, and west parts of Petersburgh and Hoosick. 
The general strike of the rocks is about N. 20° E., and the dip at various angles from 
twenty to. eighty degrees to the east-southeast. About one and a half miles from Greenbush 
on the road to Sandlake, the rocks dip in opposite directions in the same hill, the strike being 
nearly in the usual direction. 
Red and green slates are interstratified with the rocks of this group, and with the coarse 
grey and greenish grit that is supposed to be equivalent to the Shawangunk grit. It is called 
by Prof. Eaton, “ Millstone grit, and grey rubble.”* 
No fossils have been observed in the rocks of this group in Rensselaer county; and the 
prevailing rocks are slates, slaty grits and coarse grits, often very much indurated, and in¬ 
jected with veins and nests of milky quartz, and sometimes with carbonate of lime. 
Local details. It is unnecessary to specify many localities, where the rocks under consi¬ 
deration are visible in almost every mile along every road, stream, hill and valley, and where 
the dip and strike are without any great variations. Slaty grits, very much contorted, occur 
in Troy near the Catholic church. The slates, some of which belong to the Utica slate, 
occur in the banks of the Poestenkill, and in the hill on the east side of the city. The grey 
grits and slaty grits are quarried for building stone, on the hill east of Tray, and near Lan- 
singburgh. At one of the quarries (Wick,wire’s), the strata, composed of slaty grit and shale, 
are bent and distorted as represented in Plate 10, fig. 12. West mountain is mostly grit, and 
slaty grit and shale, and the latter is called by the inhabitants bastard slate. For ten or twelve 
miles in length, on the summit of the mountain, the rock is so near the surface over a breadth 
of one or two miles, that cellars and wells can rarely be dug without blasting. The water 
is supplied by springs, which are abundant. The red slate is found on the east and west sides 
of the mountain, and in some places alternates two or three timesand this and the coarse 
Eaton’s Geological Text Book, 2d edition, p. 73. 
