Mineral Contents of Quartz Rock. 



323 



lies at the northern extremity of the same elevation, is much less dis- 

 tinct. But immediately beneath this variety, the rock takes so much 

 mica into its composition as to become slaty, — almost mica slate even. 

 (No. 591.) 



In general the dip and direction of the strata of this rock corres- 

 pond to those of the gneiss and mica slate with which it is connected. 

 In Berkshire I have already remarked that the direction is usually 

 north and south, and the dip east, at rather a small angle. At the 

 quarry just mentioned, however, the dip is from 10° to 15° westerly; 

 but the buhrstone dips about as much in the opposite direction. And 

 in the quarry we find veins of granite, indicating the proximity of a 

 larger mass of that rock ; though I did not explore the surrounding 

 region for it : but I think this fact will afford a probable explanation 

 of this anomaly in the dip of the strata. In the northeast part of 

 Windsor, high up the Hoosac range of mountains, this rock dips north 

 about 25°. 



The quartz rock in Northfield and Bernardston, west of Connecti- 

 cut river, dips from 20° to 60° east, and runs north and south. East 

 of the river, its dip approaches 90° east. In Southborough its direc- 

 tion is nearly east and west, and its dip northerly and large. In Ox- 

 ford and Webster its direction is nearly north and south and its dip 

 from 20° to 45° west ; though in the west part of Oxford I noticed a 

 dip of 10° easterly, the rock being interstratified with gneiss. In 

 Sutton the dip is from 30° to 35° north, corresponding to that of the 

 gneiss in the vicinity. 



Mineral Contents. 



Scarcely any rock in Massachusetts is so destitute of simple mine- 

 rals as this ; unless we include in it those metallic veins of which 

 quartz is the gangue. And these may more appropriately be de- 

 scribed under quartz; in which rock these veins for the most part oc- 

 cur. Hematite iron ore, forming the cement of the quartzose breccia 

 in Dalton, is the most interesting mineral in the quartz rock. Sul- 

 phuret of iron, also, has been observed in small quantities in that 

 quartz rock which is associated with talcose slate in Hawley, &c. 

 In Pittsfleld, Worthington, &c. masses of quartz are found of a yel- 

 lowish color, and appear to be genuine ferruginous quartz. Some- 

 times this quartz passes into yellow jasper, and also into chalcedony 

 and hornstone, as at Dalton. 



