IQO STRATIGRAPHICAL GEOLOGY. 



wears a close resemblance to some fine grained quartzo-feldspathic granites, but upon 

 inspecting a fresh fracture with a magnifier, we instantly perceive many rounded grains 

 of quartzose sand : we perceive moreover much of the feldspar to be only imperfectly 

 formed, as if congealed when in transitit, though the mica has more nearly reached 

 the standard condition which it has in granite. In some of the coarser varieties of this 

 white rock, small distinctly rounded pebbles of quartz are to be seen, giving unequivo- 

 cal evidence, even to the naked eye, of its being an altered sandstone. Upon inspect- 

 ing many varieties of this rock, we felt no hesitation in deciding it to have been a 

 coarse silico-argillaceous white sandstone, now almost granitized by extensive meta- 

 morphic action. The slope of the steep mountain side is in many places strewed even 

 to its base, with long trains of the angular blocks of this seeming granite fallen from 

 the high crowning cliffs above. Seen in places near the summit of the mountain, the 

 rock presents two or more systems of extensive and very regular joints or planes of 

 cleavage, by which the whole mass is cut into cubical and trapezoidal blocks. This 

 jointed condition, itself so significant of an extensive internal structural change, is a 

 principal cause of the magnitude of the piles of fragments which clothe the slopes of 

 the mountain. It is beheld even more conspicuously in the shattered crests which 

 bound the valley above and below the Willey house, where an almost continuous thick 

 sheet of angular debris conceals the stratification except in the craggy precipices near 

 the summits. Those sublimely terrific and desolating slides which have occurred here 

 at different times, are therefore primarily attributable to this jointed structure. This 

 has permitted the elements to dislodge the fragments and heap an unusually abundant 

 and heavy talus high upon the slopes of the steep hills, where its unstable equilibrium, 

 weakened by saturation from copious rains, has caused great bodies of the rubbish to 

 give way and rush down with destructive impetuosity into and across the bed of the 

 narrow valley beneath. 



Generalizing the position and dip of these clearly mechanical but altered strata, on 

 both sides of the Gorge of the Saco, we think that there are ample data for inferring 

 the existence of a great anticlinal fold or axis, crossing the valley in a direction nearly 

 N. W. and S. E., as represented by the line x y. This axis is plainly indicated on 

 each side of the Gorge by a deep depression in the summit line of the mountain, espe- 

 cially in the crest which overlooks the valley on the western side. At this latter place 

 the situation and bend of the axis line is easily discernible, even from the valley below, 

 in consecjuence of the contrast of certain dark-colored argillaceous strata, in color and 

 bedding, to the other rocks. 



In the flank of the mountain, capped by the highly altered white granitized sand- 

 stones already mentioned, we discover on the west side of the Gorge, about one third 

 of a mile below the Notch and within one hundred feet of the road, a thick bed of a 

 light brownish altered shale, imbedded with a nearly vertical dip between strata of the 

 metamorphic sandstone before referred to, as so nearly granitic in its aspect. This 

 shale is replete with fossils of recognizable genera and species, but in the state of 

 casts and mere impressions. ****** 



