GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. 26 1 



Mt. Tom. On the west side of Lafayette there is an outcrop of porphy- 

 ritic gneiss at Eagle lake [Clouds], with Franconia breccia lower down 

 the mountain, having a supposed inverted position beneath the former. 

 Above both is a narrow band of Lake gneiss, succeeded by Albany gran- 

 ite, the summit being capped by porphyry. The granite is supposed to 

 occupy all the surface as far as to Redrock brook, when it is succeeded 

 by red compact feldspar. The porphyry upon Little river, east of the 

 Twin range, has a different texture and color from that on Redrock 

 brook, but is supposed to have been erupted essentially at the same time 

 with it, as well as with that upon Mts. Lafayette and Tom. The Pequawket 

 breccia occupies the summit of the Twin range, being an ejection of later 

 date than the porphyry. The Conway granite has not been certainly 

 detected on the west side of the Lafayette range, on the section line, 

 though it occurs abundantly a short distance south of it. Judging from 

 its usual topographical position, it extends beneath the Albany granite, 

 from just above the Lake gneiss, to the east slope of Little River moun- 

 tain and New Zealand river. For similar reasons, the two outcrops of 

 Albany granite upon Mt. Tom are supposed to unite beneath the slates ; 

 and the Conway is beneath the Albany series. No attempt is made to 

 show the internal relations of these several igneous rocks to each other, 

 as decisive evidence on this subject yet remains to be gathered. 



Upon Fig. 26 will be found a section from the Montalban series near 

 Chocorua pond, Tamworth, to White's ledge, north of the Saco river, in 

 Bartlett. In Tamworth the Concord granite has planes dipping five or 

 six degrees northerly; but the true position of the strata has not been 

 determined. Probably it dips at an angle of seventy degrees in a north- 

 westerly direction. The Conway granite has a fine development in the 

 neighborhood of Knowles's pond, but is less conspicuous directly upon 

 the section line back of Piper's house (p. 153), where it is situated higher 

 than the Montalban ledges. Between this outcrop and the first appear- 

 ance of the Chocorua granite, the ledges are concealed. This is the 

 place of the Albany granite, which covers a very large area to the north- 

 east of this spur. The Chocorua granite occupies all the area from the 

 end of the spur to Ellen's falls, near Swift river. The Albany granite 

 then makes its appearance, occupying the whole of the lower part of the 

 valley. It is not capped by the Chocorua granite upon the north side, 



