aw 
On the Geological Age of the White Mountains. 13 
tinctly retamed ; and at one locality we were so successful as to 
discover well characterized’ impressions and fragments of fossils, 
from which we have been able, safely as we think, to approxi- 
mate to the geological age of the strata, as well as to the epoch 
of the earliest movement of elevation. } 
At the curve in the valley, where the anticlinal axis 7 y crosses 
\ the Gorge obliquely, entering the end of the ridge already alluded 
to, and from that point down to the Willey house, the rocky 
fragments dislodged from the naked and steep slopes on either 
side, consist chiefly of a finely laminated hard sandy slate of a 
bluish color, and a coarse very compact rock of similar composi- 
tion; and mingled with these are occasionally found masses of 
the same composition, but wearing a more altered aspect, some 
_ of them containing crystalline spots and white amygdaloidal ker- 
nels, the obvious indications of an advanced stage of igneous 
metamorphosis. These fragments are extremely instructive ; for 
they exhibit nearly all the later stages of alteration, from the 
ordinary sedimentary texture to the diffusedly crystalline one. 
In some cases we see the planes or lines of sedimentary deposi- 
tion coexisting with a general but not fully perfected erystalliza- 
tion, in which however may be distinctly discovered genuine 
feldspar, augite and mica. Such specimens are to be viewed as 
an incipient hornblendic gneiss, in which through the sedimen- 
tary granular structure, typical of the secondary strata, may be 
seen everywhere and intimately dispersed, the crystallized defi- 
nite mineral aggregates equally typical of the so-called primary 
rocks. Many of these specimens seen facewise, would pass for 
genuine ancient gneiss; but looked at edgewise, they betray 
equally unequivocal marks of their sandstone nature and origin. 
Among the.more argillaceous altered rocks, are some which have 
evidently once been sandy shales, but which now consist of a 
purplish gray semi-crystalline base, imbedding several obscurely 
developed minerals. ‘I'hese rocks likewise contain serpentine, 
tale, and other silico-magnesian species, as well as some clearly 
insulated grains of crystalline quartz. 
About one third of a mile below the northern entrance of the 
Notch, on the west side of the Gorge and therefore not far from 
the extremely wild and picturesque cascade called the Flume, 
there occurs especially in the craggy summit of the mountain, a 
Srconp Sentes, Vol. 1, No. 3.—May, 1646... 53 
