ROCKS RESTING UPON A PORTION OF THE TACONIC SERIES. 
87 
III. OF THE ROCKS WHICH ARE KNOWN TO REST UPON A PORTION OF 
THE TACONIC SERIES. 
For a complete elucidation of the relations of the Taconic rocks, it is necessary that I 
should speak again of those which lie in a belt of country in the middle portion of Rensse¬ 
laer county, east of the Hudson river. This will give me an opportunity of adding to the 
illustrations of one or two interesting points in Washington county. For this purpose, I 
shall speak of the succession of rocks upon the Western Railway, between Chatham four- 
corners and Greenbush. At Chatham four-corners an unequivocal slate of the Taconic 
system makes it appearance, with the regular southeast dip and northeast and southwest 
trend. The angle of dip is high, and the rock presents that peculiar short wrinkled con¬ 
dition common to it: it contains also the milky quartz in seams. At the village, it appears 
to dip down steeply, or falls off rapidly from a modestly elevated ridge which skirts it on 
the east; and in consequence of this westerly plunge of the whole mass, the rock wholly 
disappears beneath a thick deposit of moderately coarse drift. Proceeding west from 
Chatham four-corners, upon a tolerable level way, no rock is seen in place for a mile, 
when there occurs a dark and greenish shale more or less flinty. This shale proves to 
belong to the Hudson river series; at least it contains an abundance of several species of 
Graptolites , known elsewhere in the series; it is, however, intermixed with red and 
chocolate-colored slates. These together continue half a mile, or make their appearance 
a few times in this distance; finally the thick-bedded grey sandstone appears interlaminated, 
as it so frequently is elsewhere, with fine blue slate without fossils. A succession of this 
kind continues five miles, following the railroad route; that is, there are frequent uplifts 
of the shale, and thick-bedded sandstone with its interlaminated slate. Of the character 
of this rock, there is not the least doubt: it is that which forms the northern slope of the 
Helderberg, and is elsewhere known as the Hudson river series. Now, although the dip 
is in a measure in the direction of the Taconic slate, still all sound observations show that 
it is an unconformable rock. Proceeding to Chatham centre, the succession thus far is 
clear; but after leaving the latter place, we soon come upon very thin-bedded limestone 
slate, with silico-calcareous layers and slate interlaminated, but the whole thin, and 
altogether similar to the Taconic slates. Whether these thin beds are really as I have 
supposed, is a matter of little consequence, since we soon come upon one in this direction 
of which there is no question that it is the Taconic slate. This slate continues about seven 
or eight miles, appearing only occasionally above the drift. In about five miles of the 
Depot at Greenbush, the Hudson river group succeeds; the Taconic slate again appearing 
in the form of the shales, and in that of the thick-bedded sandstone mentioned above. 
Approaching the river, the beds are more disturbed, and of a more equivocal character. 
They are not only bent, but crushed ; and a bed of siliceous limestone six or eight inches 
thick is not only broken into short pieces, but it is distributed throughout a mass of broken 
