GEOLOGY OF THE MERRIMACK DISTRICT, 529 



In the south part of Weare, about a mile north-west of Oil Mill Village, 

 is a small area of this rock, dipping 45° N. 50 W. Passing south-westerly 

 into New Boston the same range crops out at J. E. Woodbury's, near the 

 Weare line, with a north-westerly dip, and near Still pond, dipping 75° N. 

 60° W. The last has ordinary gneiss layers interstratified with it. These 

 three localities are obviously connected, and constitute an ancient ridge 

 parallel to the one previously mentioned. 



There is an outcrop of limited extent east of the Merrimack river in 

 Concord, near the " Mountain farm." The twin structure of the feldspar 

 crystals is more obvious here than at any other known locality. The dip 

 is north-westerly. It is associated with a rock like Concord granite, and a 

 small trap dike is contiguous. I judge this outcrop to be unlike any of 

 the others that have been noticed, and, if of the same age, belonging to a 

 different or parallel range. It is quite near a quartz band, of which more 

 will be said eventually. 



The amount of the porphyritic gneiss in Pelham is not definitely 

 known. When crossing the town on the line of Section I, I found in the 

 valley, from one to two miles west of Pelham village, near J. Gage's, 

 ledges of a porphyritic gneiss, but did not preserve a memorandum of the 

 dip. It probably dips southerly. There is a record, also, of a single ledge 

 of this nature by the high bridge over the Souhegan river, near the north 

 hne of Greenville. The dip of the associated rocks is 15° N. W, There 

 is another a mile west of Pratt pond. Large blocks of this gneiss occur 

 frequently in the valley of the Souhegan farther north, which may possibly 

 have been derived from the neighborhood. 



ConcliLsions. The facts stated thus far about the porphyritic gneiss 

 authorize the following conclusions : 



I. The central ridge has been subjected to such powerful pressure that 

 both sides have been inverted frequently, and we observe the fan-shaped 

 variety of stratification. A hasty generalization might state that this was 

 the newest instead of the oldest formation in the state, because newer 

 rocks apparently dip beneath it upon both sides. The same questions are 

 raised here that have been discussed for many years in respect to the 

 structure of the Alps in Switzerland. This main New Hampshire range 

 may have formed a high mountain chain in past geological time, the more 

 elevated summits having been eroded to furnish material for the building 



VOL. II. 6"] 



