80 STOCKBRIDGE LIMESTONE. 



MINERAL CONTEXTS. 



The mineral beds or veins in the Stockbridge limestone are few, and of little importance. 

 Copper and iron pyrites, ralphurel of lead in small lumps and particles, and silver in some 

 form and condition, have been long known at Singsing. The vein containing the silver 

 has not heen opened since the war of Independence. 



This rock, however, contains a large amount of oxide of iron, disseminated principally 

 at the junction of the limestone beds and slate, although the original form seems to have 

 been that of a sulphuret. From these heds the hematitic iron appears to be derived. They 

 are always tender and disintegrate rapidly, are magnesian, and frequently contain man- 

 ganese in addition to the iron. Quartz in line crystals frequently occurs either in bunches 

 or imperfect seams, associated both with albite in twin crystals, and pearl spar. 



RANGE AND EXTENT. 



The Stockbridge limestone, in New- York, Massachusetts and Vermont, trends N. 10° E. 

 Commencing at Singsing, it runs a northerly course through Westchester, Dutchess and 

 Columbia counties, bordering upon and extending into Connecticut. It passes up the 

 valley of the Housatonic, and thence over the dividing ridge into the upper valleys of the 

 Hoosic onwards into Vermont, through Shaftsbury, Arlington, and thus on towards Lake 

 Memphremagog. I am not, however, well informed as to its entire range north. From 

 personal inspection, 1 found it well developed in Arlington. At Johnson, and farther 

 north at Lake Memphremagog, are beds of granular limestone, destitute of graphite, 

 which I suppose may be prolongations of the Stockbridge limestone ; still, my examina- 

 tions have been too hasty and too imperfect among those mountain ranges, to form an 

 opinion satisfactory to myself. 



The thickness of the greatest mass of Stockbridge limestone in the Berkshire valleys, is 

 about five hundred feet. Of this thick mass, but a very small belt is suitable for marble. 

 The absolute white layers are always comparatively thin ; but by Bawing the strata through 

 the white band-, it is easy r to obtain white facings for monuments and other ornamental 

 purposes. Where the white masses predominate, silex is a very common element in the 

 rock, and therefore it frequently spoils it for the uses to which it might otherwise be 

 applied. 



\t Williamstown, Massachusetts, the Stockbridge limestone occupies all the base of the 

 first high ndsje represented on Plate XIII. Thick beds of drift conceal the rock at the first 

 terrace above the valley; but above this, the rock appears, and is well exposed up to its 

 junction with the -late that crowns all tin mountains which appear in this illustration. 

 Along the base of this mountain is a fracture whose direction is nearly north and south, 

 and the limestone forming the valley was -> \ ered from that of the mountain side by an 

 uplifting force. 



