178 
GEOLOGY OF THE SECOND DISTRICT. 
the Hudson has forced a passage through a deep gorge between gneiss on one side, and the 
Potsdam sandstone on the other, by which the junction of the rocks is clearly exposed. The 
fall is occasioned by an uplift, which, as usual, takes place at or near the junction of the two 
masses. This fact, together with that of the gradual transformation of gneiss into the Pots¬ 
dam sandstone, renders this locality an interesting place for examination. Even the partial 
development of garnet appears in the layers, after the characters of the sandstone are tolerably 
well formed. This fact is worth bearing in mind, as by it our conclusions may often be 
modified, and it is the more interesting to myself, perhaps, on account of the application it has 
to the rocks of the Taconic system ; for should I find in that system a limited extent of mica 
slate, or an alteration of the granular quartz, by which it approaches granite, I should not 
conclude that either of those masses are necessarily to be considered as varieties of these two 
rocks, any more than that the lower layers of the Potsdam sandstone at the High falls are a 
part of the Primary system. 
At the falls, the sandstone is nearly horizontal, and is about one hundred feet thick. It 
forms a good building stone, and may be obtained in large flat pieces of any dimensions which 
may be required. At the locality north and northeast of Glen’s-Falls, it is harder, and not so 
well adapted to the purposes of building. I was unable to find the characteristic fossil, the 
Lingula -, at either of these localities. 
This sandstone, as it exists in Warren, appears adapted to many purposes to which it has 
been employed in other counties, as an ordinary building stone, and probably for a fire-stone, 
hearths, furnaces, etc. For the latter purpose, it is much more likely to be found in the 
vicinity of the High falls, as it is less crystalline, or apparently less changed by proximity to 
the primary rocks. 
We should expect that a rock so near the primary would often furnish examples of frac¬ 
tures and intruded rocks, dykes of greenstone, granite, etc. I have not been able in a single 
instance, however, to find a dyke traversing this or any of the sedimentary rocks of the 
county, though they are very common in the primary rocks themselves; there are, in fact, 
but few instances in the whole district, although they every where approach near to the pri¬ 
mary mass. 
A fact attending the formation of this rock in Warren county may be stated, though it is 
not of much consequence. The lower part is a pure sandstone, to its junction with the pri¬ 
mary ; thus, at Corinth, the conglomerate does not exist, but the rock is rather an even¬ 
grained sandstone down to its junction with the gneiss over which it lies. The fact appears 
to show, that wherever conglomerates are formed, they are due to local causes ; and that 
their period is not properly one which can be termed stormy, as has been sometimes inferred. 
They may, it is true, have been formed in or during a stormy period; and so they may be 
entirely local, and formed upon a beach whose waves washed up the coarse materials, or near 
the mouth of a rapid river which bore along the larger pebbles of its shore. 
The Potsdam sandstone, no where in the bounds of this county, is charged with mineral 
matter, neither disseminated, nor in veins. The only substance which appears in it is iron, 
which is only in sufi&cient quantity to give a brownish stain. In an economical point of view. 
