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GEOLOGY OF THE SECOND DISTRICT. 
It is at this place that the Lingula antiqua is found in such great 
abundance, being common in the strata to the depth of about seventy- 
feet. It is, however, extremely obscure. Wherever it exists between 
the layers, it may be known by the dark colored lines which appear 
on a transverse fracture. It is extremely thin and delicate, and by 
far the greatest number appear only in a very imperfect state, and, 
in consequence, have been frequently overlooked, or taken for a thin 
film of carbonaceous matter. The medium in which they lived was 
one which furnished only a small amount of carbonate of lime, a 
material very essential for the habitations of all testaceous animals. 
It is the lowest and oldest fossil now known, and the genus to which it belongs has survived 
all the changes upon the earth from the era of the formation of this rock to the present time. 
The surface of most of the layers of the potsdam sandstone appears with ripple marks, 
particularly at Port Kent, where they are remarkably fine and deep. At the village of Keese- 
ville, the rock is used extensively as a building material; it is, however, the crystallized 
variety, and hence does not break so readily into those rectangular forms, as the same mass 
at the Potsdam quarries in St. Lawrence county. 
From Keeseville, it extends north several miles, but is very much concealed by beds of 
sand and gravel, such as may be seen immediately north of the mouth of the Ausable. This 
place is the most northern point in the State, upon the borders of the lake, at which the 
potsdam sandstone occurs. Towards Plattsburgh the limestone and shales of the Champlain 
group succeed, with a dip to the north; and so far as I have observed, or can learn from 
others, it does not appear between Port Kent and Quebec. Upon the northern slope, near 
the provincial line in Champlain, and also west of Plattsburgh towards Redford, it forms 
extensive and important masses, of which I shall have occasion to speak under the head 
of Clinton county. 
From the preceding observations, it will be seen that Keeseville is the most important 
locality of this rock in Essex county, both as it regards thickness and extent of surface; for 
I shall soon have occasion to speak of the continuous range of this mass, after passing into 
Clinton county. In fact, we shall find that it is one connected rock, sweeping around and 
occupying the northern slope of New-York, along the provincial line, into Franklin and St. 
Lawrence counties. 
I could not ascertain the thickness of this rock at any place which fell under my observa¬ 
tion : at the High bridge, it is known to be over one hundred feet from the water below, or 
from the river to the top of the rocks above, but this is considerably less than the whole thick¬ 
ness. I have often had occasion to notice gorges of this description, at many other places in 
this district. From present appearances, I am disposed to attribute their formation to a 
slight fracture, and upheaval of the mass in a given line or direction. Into a fracture thus 
formed, a river, from some cause or other, happens to iall: the fracture then becomes the natu¬ 
ral channel, and, in process of time, the river undermines, breaks up, and sweeps out all loose 
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