WARREN COUNTY. 
181 
Black Marble of Glen’s-Falls. 
The stratum of limestone which is here quarried, occupies a place between the Calciferous 
sandrock and the Trenton limestone. By means of a fracture or partial uplift of the rocks 
at the Falls, and by the action of the river, the three limestones have been exposed, and may 
be seen lying in the order indicated in the preceding section. The depth of rock exposed in 
this section is about sixty-five feet. On the Saratoga side, the slate which forms the upper 
part of the Trenton rock appears ; on the north side, this is wanting. The black marble lies 
under from sixty to seventy strata, varying in thickness from one inch to several feet. They 
all contain the fossils peculiar to the Trenton limestone in great abundance, but more obscured 
than at many other places. The lower part is composed of several grey layers, which are 
quarried for marble. Beneath these grey layers the black marble is found ; it is ten feet thick. 
Although some geologists embrace this mass in the Trenton limestone, yet its fossils are 
rather different, and it holds a uniform place in the Champlain group, as well as a very 
uniform thickness ; thus, at Isle La Motte, it is, as at Glen’s-Falls, immediately below the 
Trenton, and it has about the same thickness; and the same remarks may be made of it as 
it appears at Watertown, Jefferson county. It is important to keep the two masses separate 
in an economical point of view, if no other ; and as it is the only important black marble of 
New-York, it requires this distinct notice ; for it is highly probable that this very stratum is 
still more continuous than has been represented. It is true, however, that at many places in 
the Mohawk valley, it is wanting, the Trenton reposing directly upon the Birdseye limestone. 
The marble of Glen’s-Falls is worked by two companies, both of which find a ready 
market for all that can be raised ; and it is proper to remark, that it has obtained a good 
reputation in New-York, Boston and Philadelphia. One of the agents informed me that 
shelves for mantels, seven feet and six inches long, thirteen inches wide and one and a quarter 
thick, had been got out; of this size it has been sold for sixty-five cents per foot. 
There are several questions to be answered, before it is safe to enter upon the marble 
business : 
1. That relating to the expense of opening the quarry, which is by no means a trifling one. 
2. That relating to the soundness of the stone in the mass; for it is not at all difficult to procure tolerably 
sized specimens, free from cracks or flaws, and yet when the whole mass is examined, it may be 
found so fractured as to be worthless. 
3. Is the marble free from flinty layers, or flinty particles ? for even when present in small masses, they 
not only interfere with the sawing, but to a great extent with polishing. 
4. In regard to the thickness of the layers, or the mass proposed to be worked; for unless there is a 
sufficient thickness in an entire bed, or if it is divided by worthless stone, the expense of raising it is 
so much increased, that all the profits will be absorbed. When even small defects occur in a shelf, 
such as checks, a seam or crack, a little flinty matter, or a fossil mineralized by calc spar, the price 
and value is very much reduced. It is necessary, therefore, in order that a quarry should be profit¬ 
able, that it should be free generally from these defects; but so common are they, that there are 
very few beds which can be worked ^vith profit. 
