GLACIAL DRIFT. 199 
climb the steep and lofty barrier of the south spur? Nevertheless, there are indications 
of just such a change as this. 
If we place one foot of a pair of imaginary compasses on the summit of Mt. Monad- 
nock, and with the other strike a curve from the west spur to the south spur, we shall 
hardly have made a more complete change of direction from one spur to the other than 
is indicated by the striae in the short space of a mile and a half. It is difficult to pass 
over all parts of the valley between these two spurs, the upper portion of it being ex- 
tremely craggy or uneven. It is better to go down to the open pastures at the base of 
the mountain. Beginning at the foot of the western spur, and skirting the base of the 
mountain towards the east, the first thing to excite attention is the immense number of 
boulders. They exceed in multitude any other deposit about the mountain, but form 
no part of its talus, which does not fall on this side. They seem to be in some way 
connected with the change of the drift current, which began at this place, and with the 
position of the ridge, under the lee side of which they lie. Passing through these boul- 
ders, which continue for half a mile or more, we come to the first bare ledges. These 
are marked with striae N. 20° W. These are soon succeeded by others, 30°, 40°, and 
50° west of north. They may not all occur in regular order. On some ledges there 
are two or three sets of striz of different angles. Proceeding a mile and a half, we 
arrive at the easterly slope of the south spur, near the Mountain house. The road to 
this house was built north and south on sloping ground; and for half a mile the fresh 
surface of the rock was in many places exposed to view. It is everywhere scratched 
and polished. These scratches vary from 50° to 60°, and 70° west of north. Climb- 
ing the slope of the ridge, everywhere the exposed prominences of rock are embossed 
in the same direction. Arriving at the crest of the ridge, it is everywhere serrated 
and uneven. 
On this height we again overlook the whole country. Here, on the narrow crest of 
the ridge, the striz are very generally N. 40° or 45° W. In one place an angular 
trough, perhaps 20 feet long and 6 feet deep, runs across the crest. In this are long, 
continuous striz due east and west. They appear to be exceptional, and suggest the 
idea that this shallow trough had been able to control and change the direction of the 
striating force. Standing on this ridge, and looking towards the east, we see that the 
mountain on this side is very precipitous, and that probably there are no striz on its 
broken surface. Higher up the mountain, within a thousand feet of the summit, the 
strie are 35° and 30° west of north; lower down, at the extremity of the south spur, 
the end of the long dam, they vary from 40° to 25° west of north. What kind of striz 
should we expect to find under the lee of this four-mile breakwater? Another expedi- 
tion and another day were required to answer this question. The country east of the 
four-mile ridge is mostly wooded and difficult to traverse. The rock is mostly covered 
by drift. Beginning at the south end, and travelling north, no striz were found until 
two thirds of the distance had been passed over. Curiosity was at last gratified by 
finding large, flat surfaces of naked rock, scored all over with long parallel lines much 
better preserved than those on less wooded and more exposed parts of the mountain. 
