STOCKBRIDGE LIMESTONE. 155 



Tliis limestone is distinctly enclosed in the magnesian slate, and it is not possible to dis- 

 cover any difference of the slate on either side of the limestone : it is, in fact, one rock in all 

 respects. The limestone commences with a few alternations of slaty layers, when the former 

 soon appears well developed, and it disappears in the same manner. The thickness of the 

 beds or layers varies greatly, being from one or two inches to two feet. It is often interlami- 

 nated with talcose matter ; but this is sometimes so much diminished, that the layers appear 

 merely sprinkled with flakes of talc. The following section e.xliibits the New-Ashford marble 

 quarry in Berkshire county, Massachusetts : 



50. 



1. Allernalion of slate and limestone. 2. Layer of pure limestone. 



There is no question, in this case, of the true relations of this limestone, and of its being 

 enclosed in the slate ; and no doubt of its stratification, or of its being a sedimentary rock. 

 Its eastern inclination is about 30° ; and the quarry appears like a simple uplift, free from 

 contortions or other disturbances which derange the strata. 



The thickness of the whole quarry of limestone, of which I have given a section, is about 

 three hundred feet. Of this mass, but a small portion can be worked as marble ; and it is 

 often the case that a single stratum, not over two feet wide, has to be pursued alone, in order 

 to obtain the blocks of a suitable size. Under these circumstances, immense quantities of 

 mere stone have to be raised and removed to secure the object aimed at. It is, however, some- 

 times the case, that the adjacent layers form an inferior marble of some value ; a very large 

 proportion, too, forms a good building stone, and an excellent material for lime, which to a 

 certain extent are found useful. 



There are several narrow belts of limestone which traverse the Hoosic valley from north to 

 south ; and it is a question of much interest to decide, whether those several bells are so 

 many distinct masses, or whether they are the same, which are brought repeatedly up by an 

 uplift. From inspection they appear to be different masses, so far as the character of the 

 strata are concerned. We may safely consider, that there are at least two distinct belts of 

 this limestone, one of which lies close upon the Hoosic mountain, and is in some parts quite 

 coarse, in others rather fine, but in beds whose structure is much like gneiss. The latter is 

 a very inferior limestone ; in fact, when it desintegrates, it often leaves a distinct skeleton of 

 silex of the original form ; the hmestone is apparently dissolved out, and the silex remains in 

 a light porous mass. The other belt passes through the central part of Berkshire county, 

 approaching occasionally the New-York State line. In some localities it is associated with 

 granular quartz, and lies on both sides of it, dipping beneath it on the west side, and reposing 

 upon it on the east. 



