160 



GEOLOGY OF THE SECONn DISTRICT. 



Another importaTit mass of granular quartz, in this last range, appears fifteen miles south 

 in Dalton, in close proximity with the primary of the Hoosic mountain range. Monument 

 mountain, in Stockbridge, is another great mass of this rock ; and still others exist. All the 

 examples of diis rock arc insulated, or surrounded by other rocks, as if they were great beds 

 in the latter. 



The stratification of this rock is more or less obscured by the crystallization of its layers. 

 It furnishes but few instances of contortion, while, as has been stated, they are extremely 

 common in the limestone which lies in immediate contact with it. One beautiful instance of 

 curvature and fracture has been noticed in this rock in Williamstown, on the west side of the 

 hill opposite the burying ground. The section No. 52 is a representation of the fracture and 

 curvatures here referred to : 



This curious and highly interesting case of contortion occurs in the western slope of the 

 hill. The strata dip to the east as usual ;* and this mass of quartz, which is more slaty than 

 usual, lies between two beds of limestone. In this instance, there is the uplift accompanied 

 with the effects of lateral pressure, which formed not only a double arch, but here so power- 

 ful as to break the mass nearly in the centre between the two arches, and the portion on the 

 north side is thrust up so as to override and overlap the other. At the line of fracture, the 

 surface is partly crushed and partly rolled into short cylindrical pieces, giving at the same 

 time to the adjacent laminc-e many short and unequal curves. 



This I take to be an instance in which the flexures of the strata have been really produced 

 by lateral pressure : it certainly does not belong to a doubtful case, in consequence of the 

 fracture the layers have sustained. In this instance, however, it would seem that the pres- 

 sure was confined to a few feet thickness of rock ; for from what appears, about eight or ten 

 feet was raised uj) from the strata beneath, and to these few layers the pressure might have 

 been confined. There is at least a small cavern or space beneath, which seems to have been 

 formed by raising up the strata forming the roof, from those which form the floor. 



The granular quartz is the least regular in its occurrence, of any of the rocks of the Ta- 

 conic system ; it generally appears in insulated mountains, surrounded apparently by other 



♦ The preceding cuts, Nos. 19, 50, 51 and 53, were not reversed by llic engraver, and hence the dip and other cliaracters are 

 misrepresented. 



