. GEOLOGY OF THE WHITE MOUNTAIN DISTRICT. l6l 



It would be properly in order next to take up the laijradorite rocks, 

 and the porphyries occupying the area inclosed l^y the granites just de- 

 scribed. Inasmuch as a little more investigation is required for their 

 satisfactory description, I will depart from the established order, and 

 present next a full account of the rocks recently dispb^yed by cuttings 

 along the Portland & Ogdensburg Railroad, in the White Mountain 

 Notch, followed by abundant citations from the best authors who have 

 written anything concerning the geology of the White Mountains. 



The Rocrs in the \yiriTE Mountain Notch. 



I propose now to describe carefully the outcrops of all the formations, 

 mostty not alluded to before, cropping out along the route of the new 

 railroad between Fabyan's and Bern is station, vvdth any new information 

 I may happen to have about the adjacent mountains. The slates of this 

 region have not yet been described, and I shall therefore anticipate that 

 part of the chapter. The following sketch is mostly the result of obser- 

 vations made in July, 1875, undertaken for the purpose of testing the 

 value of theories suggested in the earlier part of this report. There is a 

 somewhat triangular area occupying the Ammonoosuc valley first requir- 

 ing attention. It is bounded east and south-east by the range of presiden- 

 tial summits, which are all of the Montalban series ; west, by the Field-Tom 

 line of elevations, extending to the Ammonoosuc river, and north by the 

 Cherry-Deception-Dartmouth group. The land is everywhere compara- 

 tively flat, as compared with the mountainous border. The difference is 

 excellently set forth in the heliotype showing the Mt. Washington range 

 from the Fabyan turnpike. Volume I, p. 392. Two sorts of granite 

 occupy the whole of this low country. The first is much like that of 

 Concord, well seen along Section IX. It is tender, friable, with a nearly 

 uniform texture. The second shows crystals of feldspar, porphyritic and 

 extensively elongated. Its most conspicuous localities lie along the east 

 border of the valley from Mt. Dartmouth across to the base of Pleasant. 

 It protrudes through beds of the Montalban schists at the base of Mt. 

 Pleasant, as well as constituting an extensive area by itself. This fact, 

 however, shows its age. This area is probably continuous westerly 

 across to the Portland & Ogdensburg Railroad, a mile north of the 

 Crawford house, where it crops out in a small stream. Between the 

 VOL. 11. 21 



