6o8 STRATIGRAPHICAL GEOLOGY. 



west edge is touched. At M. M. Potter's it has the average coarse text- 

 ure. At M. Leavitt's, at the crossing of the road by the brook emptying 

 into the lake, is a very coarse and singular breccia, requiring further 

 examination. The coarser sienites occur as nodules in a rock resembling 

 trap, and the jointed planes dip westerly. A chmb to the pond on the 

 ridge south of Gunstock mountain shows the fine-grained variety predom- 

 inating on the way up, and also on the mountain to the east. Between 

 the water-shed in the road to West Alton and M. Leavitt's are several 

 of the brecciated outcrops. A climb of the south end of the mountain 

 shows us ferruginous mica schists and indigenous granite, and next the 

 sienite indurated schists dipping 80° N. 35° W. towards the south-west 

 spur of the former rock. The rock of the mountain is like that on the 

 northern peak, just described, and with similar accessories. The rock 

 has a reddish cast. Joints cut each other vertically, running north-west 

 and north-east. The summit rock is somewhat porphyritic, from the 

 presence of feldspar crystals. The sienite was not reached till we passed 

 up Mt. Straightback in Alton, at some distance beyond the end of the 

 carriage-road. In a large ledge one can see the sienite and porphyritic 

 gneiss joining each other, Avery hill is of sienite. Quite a large piece 

 is taken out of the sienite area here by the presence of porphyritic gneiss 

 and mica schist. The junction of the first with the sienite is well shown 

 between Avery hill and Pine mountain. The line of junction is vertical, 

 running east and west. The latter summit is probably of sienite, but has 

 not been visited. The two Rocky mountains are composed of the ordi- 

 nary variety of sienite. With them the rock terminates, and the country 

 becomes comparatively flat. The Rocky and Pine mountains, with Avery 

 hill, constitute a semicircular ridge like the half of an amphitheatre. The 

 best part of this sienitic area is away from the travelled roads, in the for- 

 est country, so that the facilities for its understanding are not good. 

 Diamond island, in Winnipiseogee lake, is made up of a fine-grained 

 sienite ; and it is presumed Rattlesnake island is composed of the same 

 material. Scarcely any of the islands at the south end of the lake have 

 been examined. 



The Red Hill and Belknap sienites obviously belong to the same age, 

 as they are so much alike. They are both very free from admixture with 

 granites. The Tripyramid and Jackson sienites are to be allied with 



