322 



Scientific Geology. 



however, this rock lies generally at a low level ; corresponding in 

 this respect with the limestone. The largest proportion of this rock 

 is gray or reddish granular quartz. In Cheshire it is extensively 

 disintegrated, so as to form a good sand for the preparation of glass. 

 For the cause of this disintegration I have sought in vain. The 

 buhrstone in Washington, near Pittsfield, is another interesting vari- 

 ety; and in the same hill the granular quartz is quarried extensively 

 for architectural purposes, on account of the great regularity of its 

 stratification. I observed the variety containing mica, in Lee, Wash- 

 ington, Canaan, Ct. &c. ; though this is not the most common variety. 

 The situation of the breccias and conglomerates has been already 

 pointed out. 



It is also unnecessary to say any thing farther in relation to the 

 quartz rock containing talc and hornblende. 



In connection with the gneiss in the southeastern part of the State, 

 it may be remarked, that quartz rock occurs in considerable quantity, 

 as I have noticed in several places, having an agatized structure. 

 That which I found in Rochester, is quite beautiful, (a polished speci- 

 men of which may be seen in the collection.) Some examination 

 since the publication of the first edition of the first part of my Report 

 has led me to suspect that this quartzose aggregate is more abundant 

 and extensive than I had supposed ; perhaps extensive enough to de- 

 serve a place on the map. 



Dip, Direction, and Character of the Strata. 



It requires in many cases careful attention to discern seams of stra- 

 tification in the purely granular quartz of Berkshire county. They 

 are never, however, wanting for any considerable extent. And very 

 frequently there exists a set of cross seams, nearly at right angles to 

 the planes of stratification. The same thing is true of the quartz 

 rock of Leverett and Northfield, in which mica is sparingly interlam- 

 inated. (No.577.) 



In general, however, quartz rock exhibits great distinctness and 

 regularity of stratification, particularly the variety last mentioned. 

 Where the mica is in small quantity, the thickness of the strata is 

 considerable ; but as the mica increases the layers are thinner, until 

 al length the rock becomes schistose. At the quarry in Washington, 

 near the buhrstone locality, the stratified structure is beautifully exhib- 

 ited ; and it results from a minute quantity of mica, in scales scarcely 

 visible to the n?ked eye. The stratification of the buhrstone, which 



