626 PHYSICAL GEOGRAPHY. 



mack. Still farther to the south, the aspect of the Saco valley appears 

 in the heliotype which shows Mt. Crawford, over Dr. Bemis's house, at 

 Bemis station on the railroad. This is the last of the granite elevations 

 on the east till Wilkes's ledge is reached, represented opposite page 220, 

 in company with a view of Mt. Pleasant. The mountains on the west 

 side are granitic throughout, the schists below Mt. Crawford consti- 

 tuting an island. 



We are now prepared to understand the origin of the Notch. It has 

 been excavated almost entirely out of granite. It lies near the eastern 

 border of the vast sheet of Labrador granites heretofore described, per- 

 haps on the line of eruption. This deep valley exists for the reason that 

 the denuding agents have excavated it out of the softest materials occur- 

 ring in this vicinity. The summits of Mts. Webster and Willey consist 

 of flinty slates, which resist decomposition much more steadfastly than 

 the intervening granite. A climb up both these mountains shows that 

 the granite extends nearly to their summits. In descending, one finds an 

 abundance of loose, friable rocks, inclined at the greatest angle possible 

 for such materials. These fragments accumulate gradually through the 

 action of frost, and, under favorable conditions, when rendered pasty by 

 abundant rains, make a kind of plastic material which slides to the bot- 

 tom of the valley, where the river disintegrates it still further, and carries 

 it towards Conway. The plains below Bartlett are largely composed of 

 the fragments brought down from this narrow valley. The Saco valley 

 below Mt. Webster is lower, because the walls are composed entirely of 

 this softer rock, and have yielded readily to the forces of disintegration. 



The excavation of the broad valley of the Ammonoosuc to the west 

 of the Washington range, bounded northerly by Mt. Deception, and 

 southerly by Mts. Pleasant, Clinton, and Willard, is to be explained in 

 the same way, only the materials have gone down towards the Con- 

 necticut instead of the Saco. The harder ridge remains on the east. 



Other Varieties of Rock Sculpture. 



Of the other shapes fashioned by Nature, the isolated, conical schis- 

 tose mountains are the most unusual. Such are Monadnock, Kearsarge, 

 Ragged, and numerous smaller eminences rarely heard of, like Peaked 

 mountain in Piermont. Their peculiarity consists in the rising up from 



