84 BROWN SANDSTONE, 



Another variety is worthy of notice ; it is a species of porphyritic sandstone at the inferior 

 part of the rock. The felspar is in small angular forms, and very liable to decompose ; 

 and having disappeared in this way, the quartz is left in a porous rough state resembling 

 the Paris burr stones. The dip and strike of the beds usually conform to the other rocks 

 in the system, being from 20° to 45° E., and some beds are vertical. This rock is rarely 

 thin-bedded, and so strongly marked are the transverse natural joints that the bedding 

 planes are often nearly obliterated ; the planes are, however, often distinguishable by 

 laminae of siliceous slate. 



The Granular quartz is the least regular in its continuation of any of the rocks of the 

 Taconic system ; it generally appears in insulated mountain masses, surrounded apparently 

 by other rocks ; still, taking the range of our system as a guide, we find it prolonged far 

 to the north and south, though not continuously. 



Some facts have led me to indulge for the present the opinion that two distinct masses 

 exist in the Taconic system : one adjacent to the western base of the Hoosic range ; the 

 other, still farther west. The former is the most persistent and important, and rises into 

 mountains from twelve to fifteen hundred feet high. Such is Oak hill, between Adams 

 and Williamstown, Massachusetts ; also in the east part of Bennington, Vermont ; and 

 Monument mountain, in the south part of Berkshire. 



Mica is extremely rare in granular quartz : its surfaces are often sprinkled with talc. 

 It is sometimes interlaminated with a dark siliceous slate, but these laminae rarely exceed 

 half an inch in thickness. It passes, however, into a rock of this character, and forms a 

 tolerable flagging stone. ■ 



This rock, from its extreme hardness,- resists the comminuting agents which destroy 

 other rocks ; and hence, in the vicinity of its beds, the cobblestones are usually very 

 abundant, and fill the soil to a great depth. These soils, therefore, are often worthless, 

 from the impossibility of removing the stones. Where only a moderate quantity of this 

 kind of stone is present, the land is of excellent quality, and well adapted to corn and rye, 

 particularly the latter. 



Some difference of opinion exists in regard to the system to which the granular quartz 

 belongs. Prof. Hitchcock places the rock in the Gneiss, or Primary schists. He remarks, 

 si^eaking of the topography of the rock, " I luive represented all the quartz rock in the 

 State as associated with mica slate, talcose slate or gneiss. It is more or less connected 

 with other rocks, as with limestone in Berkshire, and with argillaceous slate in Bernardston. 

 But in all other cases, except in regard to gneiss and mica slate, it is little more than a 

 juxtaposition of the two rocks ; whereas the quartz rock alternates with, and passes imper- 

 ceptibly into, gneiss and mica ^ate ; and, in fact, it might be regarded very properly as a 

 meml>cr of tlio gneiss and mica slate fornuUions."* 



I am unaljle, from the perusal of the above extract, to satisfy myself that the different 

 beds spoken of are not in reality of different ages. Whether this suggestion is true or not, 



• Massachusetts Report, pp. 589-590. ' 



