GEOLOGY OF THE MERRIMACK DISTRICT. 509 



nearly continuous, and a brook near the line of Keene and Swanzcy 

 crosses it, but it does not extend far into Swanzey. 



In Chesterfield, near C. A. Lincoln's, we have small veins of quartz ; 

 and at the forks of the roads south of J. Putnam's the veins have consid- 

 erable width, and contain many cavities with quartz crystals. Here, as 

 elsewhere, the quartz penetrates the protogene gneiss. This locality is 

 the southern limit of this peculiar vein quartz, as far as we have been able 

 to trace it. 



From our study of this rock we conclude (i) that these veins are 

 endogenous, i. e., the material of which they are composed was derived 

 from the adjoining rocks and from the deeper parts of the fissure ; 

 (2) that the vapor or solution from which the silica was deposited was 

 strongly alkaline, — so much so that in some cases it absorbed the silica 

 of the adjacent rock ; and that this was re-deposited with that already 

 held in solution, enclosing portions of the feldspar of the county rock. 



Granite. There are seven well-marked areas of granite in this topo- 

 graphical district. The boundary of each, however, does not seem to be 

 so regular as that of the areas of granite in the central and eastern part 

 of the state. Here, except that in Roxbury, the areas are much longer in 

 the general direction of the strike of the rocks of the country than across 

 it. At Sunapee and Fitzwilliam they differ not only from those east, 

 but also from others in this district, by having several different kinds 

 of rocks immediately associated with the granite. 



Specimens of rock from different localities vary in the coarseness or 

 fineness of their mineral constituents rather than in their composition ; — 

 at least, examining the specimens with a common lens, about all we can 

 say is, that one is coarser or finer than another; but microscopic analysis 

 may show much greater distinctions. 



The most northern area is in Rumney. Immense boulders of the gran- 

 ite lie along the side and at the base of Rattlesnake mountain. These 

 boulders are quarried ; and it is wonderful how they have withstood the 

 action of the atmosphere through the ages that they have been exposed 

 to its influence. Many of them are scarcely affected by weather, showing 

 that it is one of the very best of our granites. North of Quincy station 

 there are ledges of granite, but the rock seems to be of a different char- 

 acter, more quartzose, and not so suitable for working. 



