224 STRATIGRAPHICAL GEOLOGY, 



granite comes in contact with the porphyry, it is full of distinct crystals 

 of orthoclase and quartz, just like the rock on Mt. Willard next the slate 

 breccia. The porphyry upon the top of Mt. Flume seems to slope north- 

 erly. 



Between this ridge and the Franconia branch there is an area of twenty 

 or more square miles, — concerning which we have no information, — sup- 

 posed to be occupied mainly by the Albany granite. 



Twin Mountain Area. 



This comprises, first, the broad, elevated range between the most 

 northern of the Twin mountains, and well on to the south end of the 

 higher part of the mountain mass, about three miles in length ; second, 

 a long ridge on the west, between the Franconia and Redrock brooks ; 

 third, a north-easterly extension into Little River mountain (or perhaps 

 the latter may be isolated); and, lastly, a development on the east to in- 

 clude the divide between Little river and New Zealand pond. 



From the side of the long, elUptic-shaped ridge on the west towards 

 Franconia Branch, we have specimens of Albany granite, but finer-grained 

 porphyritic varieties near the summit and the east side. The stream on 

 the east side, in descending from the west slope of South Twin, falls over 

 abundant ledges of red compact feldspar. Boulders from this locality are 

 strewn from here to Mr. Pollard's house in Lincoln, especially between 

 the mouths of the Franconia and Hancock branches. Their prominence 

 has suggested for this stream the name of Redrock brook. 



There are several varieties of the porphyry on the summit of the South 

 Twin. The most common is fine grained, drab-colored, with reddish crys- 

 talline spots, all of it probably orthoclase, though at first sight suggestive 

 of labradorite. Our best specimen from this locality shows a few crystal- 

 line grains of clear quartz in the drab portion ; and there are bunches of 

 reddish-gray porphyry intermixed, holding the same red orthoclase bits 

 with the darker portions. In the descent towards Little river, on the 

 way to New Zealand pond, the rocks are varied with a sprinkling of 

 something like Chocorua granite. The felsite contains much quartz, and 

 a few small masses of a decomposing, dark greenish mineral. Somewhat 

 lower down Little river than its crossing, on the line of description, there 

 is a reddish granite. On climbing the ridge east of the stream, the slope 



