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EXPLANATION OF THE PLATES. 
PLATE XVIII. (TACONIC SYSTEM). 
Section 1. The valley of the Hudson is formed at Fort-Edward by the Hudson river series. The hills 
bordering- the valley are often crowned, as represented in the plate, by the calciferous sandstone, 
beneath which we invariably find the taconic slate. The calciferous sandstone is usually an outlier, 
and is really an insulated mass. Proceeding eastwardly, the slate is known to contain beds of 
grit and sometimes calcareous strata, which are usually, if not always, thin-bedded and without 
fossils. The thick and heavy beds of limestone are found only towards the base of the Green 
mountain range. The granular quartz, or brown sandstone, is the most eastwardly rock of this 
system, and rests, in this section, on gneiss. The drift obscures the relations of these rocks towards 
Sunderland, but there is no doubt respecting the superposition of the granular quartz. This section 
may be regarded as one of the best for exhibiting and proving the entire independence of the Taconic 
system from the Primary below and the New-York system above. 
Section 2. This section furnishes some facts of an interesting kind. The bordering ridge of the Hud¬ 
son valley is crowned, east of Greenbush, with a mass of calciferous sandstone, which abounds in 
its peculiar fossils; but the superior part of the limestone is the Trenton, which finally passes into 
a black slate, which also contains fossiliferous layers of limestone; so that we are furnished at this 
point with slate above identical with the Trenton slate, and also slate below identical with the 
Taconic slate. None but prejudiced geologists will have the hardihood to maintain that the slate 
beneath the calciferous sandstone is equivalent to the Trenton or Utica slates, or the slates of the 
Hudson river group; or that the series has been reversed or overturned. Upon this section the 
Hudson river group recurs, beneath which lie the taconic slates. At Chatham four-corners, the 
taconic, or perhaps more properly the magnesian slates emerge from beneath the Hudson river 
group which appears about a mile west, the intervening space being filled with drift. 
Section 3. The west end, at Whitehall, exhibits the lower rocks of the Champlain division resting 
upon gneiss. The former are deeply cleft by diluvial action. The taconic slates appear for the 
first time about three miles to the east, and in many places in this region they support the outlying 
masses of the calciferous sandstone. The section extends between five and six miles east of 
Whitehall. 
Section 4. This section exhibits nearly the same phenomena and geological relations as the preceding. 
Section 5. This short section is designed to exhibit the relations of the superior mass of the Hudson 
river group to the taconic slates. The thick bed, however, is succeeded by a thin-bedded slate. 
The thin-bedded limestones occur a few miles from Bath on this section. 
Section 6. At Poughkeepsie taconic slates appear in the steep bluffs which line the banks of the river. 
At Milton, about one mile west of the landing, the Hudson river group appears, and contains the 
common fossils of the series. The dip is changed in this case to the east. The layers are closely 
packed, and the fossils consequently are obscure. 
PLATE XIX. 
Platerskill Clove. It is a deep cut in the Catskill mountains, through which there is merely space 
for a road. The view is eastwardly, and looks out upon the Hudson valley, in which the river may 
be seen threading its silver way to the Highlands. Beyond, the Taconic ranges rise and meet the 
horizon in elevated panoramas. The rocks which appear in the notch or clove, belong to the 
Devonian series, and lie in horizontal position. They have been cut down nearly a thousand feet 
by diluvial action. Numerous primary and foreign boulders are lodged in this narrow passage, and 
show conclusively the transporting agents which have been at work in ancient times. 
