WARREX COUNTY. IRl 



Black Marble of Glen"s-Falls. 



The stratum of limestone which is here quan-ied, occupies a place between the Calcifevous 

 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 jjreceding 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 gi-ey 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 gi^oup, as well as a very 

 uniform thickness ; tlius, 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 Waterto^Ti, 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 si.xty-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, wliich 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 verj^ 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 with profit. 



