GEOLOGICAL RELATIONS. 29 



of an extensive field, not less than four hundred square miles in extent. The Albany 

 granite, or the second horizontal layer, is thinner than the first in this locality, but is 

 as thick in other parts of the basin. Both the granites are thinner at this outer edge 

 of its area, and thicker in a westerly direction, the first to the greatest amount in Bart- 

 lett, along the section line. Above the Albany granite are found two masses of clay 

 slate, somewhat indurated and much contorted, the one on the south and the other on 

 the north side of Pequawket. These are of too limited extent to find place on our 

 section, but are important in the history of the mountain. The formation is identical 

 with the andalusite slate on the east side of Mt. Washington, represented in the Plate. 

 It is to be presumed that the outcrops were formerly directly connected, though their 

 nearest exposures are certainly ten miles removed, the disappearance being probably 

 due to denudation. This slate is apparently much more modern than the Conway and 

 Albany granites, possibly of Paleozoic age. 



The igneous material of the upper and principal portion of Mt. Pequawket is more 

 recent in origin than this slate, since fragments of the slate are disseminated through 

 it. The lower portion is mostly a breccia, made up of the slate fragments, which grad- 

 ually diminish in quantity in ascending the mountain. The igneous paste is feldspathic, 

 and approaches the Albany granite in lithological structure. The same granitic rock 

 composes the main bulk of the Mote mountains, on the opposite side of the Saco river. 

 Very likely the two mountain masses were connected at the time of the eruption of the 

 unstratified material, and the broad valley between has since been excavated by atmos- 

 pheric agencies. No other localities of this Pequawket granite have been discovered, 

 save a few feet thickness of breccia on Mts. Willard and Tom, near the Crawford 

 house. 



The Montalban schists, from Jackson to the west base of Mt. Washington, have a 

 north-westerly dip, with innumerable local contortions. I advocated the doctrine that 

 Mt. Washington is an inverted anticlinal, in the annual report of progress for 1870. A 

 collation of all the dip observations upon the mountain indicates the presence of a few 

 easterly inclinations upon the eastern side, where erosion had spared the upper layers. 

 A common phenomenon is the occurrence of a low, undulating, south-easterly dip, ob- 

 servable for several rods, which changes suddenly into a nearly vertical north-westerly 

 pitch, folding underneath the first. When we descend into the deeply excavated 

 ravines of Tuckerman and Peabody river, west branch, the latter inclination is the com- 

 mon one, since the surface undulations have been washed away, and only the folded 

 strata remain. This phenomenon occurs mainly in the andalusite slates, as seen along 

 the carriage-road. Full details concerning the variations will be found in the descrip- 

 tion of Section IX. Furthermore, the general position of these evidently newer slates 

 is monoclinal, with no corresponding repetition, on the eastern side of the valley, of 

 similar strata exhibiting a dip in the opposite direction, as would be expected should 

 the theory of a folded axis be set aside. 



At the west base of Mt. Washington is a large amount of granite, carrying long, 

 slender crystals of orthoclase, which give somewhat of a porphyritic aspect to the rock. 



