J 28 STRATIGRAPIIICAL GEOLOGY. 



chiefly to the changes in the strike and dip of the strata. While in 

 general the strike is not very far from north and south, there are many 

 notable exceptions. The most marked is at the head of Cold river, where 

 the strike is nearly east and west, and the dip is north, nearly vertical. 

 A change in the strike causes the mountain ridge to sweep round in 

 a curve towards Baldface mountain. Between Ellis river and Wildcat 

 branch there is a sharp mountain ridge that runs nearly north and south, 

 extending down from Wildcat mountain. This ridge has in places a 

 height of two thousand feet. East of Wildcat branch there is a ridge, 

 including Black mountain, that is somewhat higher than the last. The 

 other well-marked heights in Jackson are either granitic gneiss or in 

 part intrusive rocks. 



The rocks of Bean's Purchase, Chatham, and Jackson are for the most 

 part quite uniform. The entire range east of the Glen road, including 

 Mts. Moriah, Imp, Carter, and Wildcat, is composed of the White Moun- 

 tain gneisses. These rocks extend from this ridge eastward into Maine ; 

 and the mountain ridge including Mts. Royce and Baldface is the same. 

 The rock in the area between Baldface mountain and the site of the 

 Dearborn & Philbrook saw-mill is a feldspar-porphyry, with a limited 

 outcrop of a dark-reddish, more compact feldspathic rock on the south- 

 west side of Sable mountain. This last has sometimes the appearance 

 of being a breccia, and resembles the feldspar-porphyries of Mote moun- 

 tain. Though not seen in many j^laces, it probably extends southward 

 to Mountain pond. Both south-west and north-east from Mountain pond 

 the rock is a reddish granite. Slope mountain is probably its limit north- 

 ward. South of Chatham Centre we find a granite very similar to that 

 of Conway, while in the north-east part of the town, north of the Cen- 

 tre, the rock is generally the gray micaceous gneiss of the Montalban 

 group, though on the east side of Baldface a granite has been quarried 

 that contains quite a large proportion of feldspar. The dip of the gneiss 

 is quite variable. Half a mile north-west of Chatham Centre it is N. 3° 

 E, 68°. Just above the school at the base of Slope mountain the dip is 

 N. 37° E. and E. 56°. It has been affected here, no doubt, by a great 

 granite mass on the west. On the south slope of Mt. Royce, where an 

 observation was taken, the dip is N. 13'' W. 20°; but, from the precipi- 

 tous character of the mountain, the inclination of the strata must be 



