MUSEUM OF COMPARATIVE ZOOLOGY. 81 
West Peak sheet. The trend of the western face of Notch Mountain is 
N. 50° E., and it may be traced in a more or less distinct bluff or ledge 
(12) for a mile in this direction. On following up the intercepting 
canal cut in the trap to bring the streams from the back of West Peak 
into the north end of the reservoir, a band of breccia about a foot wide 
may be found traversing it, trending N. 60° E.; and the back of West 
Peak is furrowed with ravines (13) trending N. 55° or 60° E., showing 
that faults of the normal direction occur here as well as to the east of 
the reservoir. The general topography leading to the above conclusion 
~ may be perceived from a knoll (15) a good half-mile northward. The 
long northwestern face of Notch Mountain is from here clearly seen to 
be independent of the detached portion (14) of the West Peak block. 
A low trap ridge (16), a little to the west of the knoll, is probably to 
be identified as the posterior sheet of the same block. 
The abnormal position of the reservoir valley finds no sufficient ex- 
planation. It may be located on a branch of the chief fault; but in 
such case the chief fault ought to be the site of the chief valley, and 
not merely of a little ravine. Perhaps a more likely explanation will 
some day be found by regarding the reservoir valley as the abandoned 
course of an old river, whose direction was taken during the pre- 
cretaceous base-levelling of the region, and maintained for a time after 
the post-cretaceous elevation, until some other stream, which en- 
countered no heavy trap sheet and therefore deepened its channel 
quickly, captured and led away the head waters of the reservoir river ; 
the reservoir notch would thus fall into the class of wind gaps derived | 
from water gaps, not uncommon in the Appalachians. But different ob- 
servers may well have different opinions here. 
While on the knoll (15), the double form of Notch Mountain will be 
observed. A second trap sheet (17) seems to lie on the back of the 
first. (It is rather too distinctly drawn in Fig. 11.) The same thing 
might have been noticed from the back of the anterior sheet of Cat Hole 
block, where the roads form alittle triangle. A rough walk through the 
woods around the base of the upper sheet (17) to Cat Hole shows the 
back of the lower sheet to be highly vesicular; a rocky talus hides 
the contact between the two. I have interpreted this as the topo- 
graphic expression of the two lava sheets disclosed in the quarry bluff : 
the vesicular upper part of the lower sheet acts as a soft bed between 
the denser parts of the two flows, and the mountain grest is therefore 
doubled. The same double form may be seen in the mountains of 
Medina sandstone in central Pennsylvania, and for a similar reason. 
VOL, XVI.—NO. 4. 6 
