198 SURFACE GEOLOGY. 
less regular than the points of a star, yet present to four points of the compass 
long ranges of bare rocks, which have recorded the markings of the ice-period, with all 
their variations of direction, and furnish a lesson not to be found, perhaps, in any other 
locality. To understand fully the meaning of the evidence herein detailed, it is neces- 
sary to have a clear idea of the relative bearing and position of these radiating ridges 
or spurs. 
For the sake of clearness of description, we will suppose the principal ridge, which 
runs N. 25° E., to be straight, and to be four miles long. This ridge was an uplift, 
sloping towards the west, and presenting its broken and precipitous face towards the 
east. Itis like a dam set obliquely across the current of the northern drift, and its 
serrated edge rises from 1,500 to 2,000 feet above the surrounding country, growing 
higher from each end to its central parts. If we suppose a section of this range near 
the centre to be pushed some fifty rods further west, and elevated to the height of 3,280 
feet, we shall have the summit of Monadnock. A short spur projects west of the sum- 
mit about a mile, and divides into two branches. These we will call the west and 
north-west spurs. The two ends of the dam we will call the north and south spurs; 
these, with the western spur and its north-west fork, complete the outline of the moun- 
tain, making four radii. 
Numerous observations of the direction of drift striz made in the adjoining towns 
show very general uniformity. They have a range of not more than 15°, varying 15° 
west of north to north and south. On the summit of Monadnock the direction varies 
within the same limits. Only one set of strize was noted there as 5° east of north. So, 
too, following along the north-east spur, there is no change in the striz so long as the 
altitude remains the same. The crest is all naked rock for two and a half or three 
miles, and frequent observations can be made. Just as fast as the ridge falls off in 
height, the stria gain a more westerly direction, becoming 15°, 20°, and 25° west of 
north; where the rocky ridge terminates and is succeeded by open pastures, 30°, and 
in many places 40°, were noted as common. Appearances indicated a local deflection 
of a current around the northern end of this long dam. 
Although a special expedition was made to what was called the north-west spur, the 
lower portion of it was so much covered with drift that few exposed places could be 
found. Some five or six, however, and all that were noted, showed strie N. 25° E. 
All the higher portions of the ridge were striated like the summit and the ridge before 
described. 
Another day’s expedition was made to the west spur. Standing on the crest of this 
lofty ridge, and looking towards the south, the view is unobstructed to the horizon. 
The striz all along this ridge are innumerable, and all north and south. There is no 
opposing ridge near, to lead one to expect south of this a change in the stria. On the 
contrary, there is every facility for the drift current after passing this ridge to continue 
on ina straight course. The southern spur is a mile or more off on our left, and pre- 
sents a high opposing barrier towards the south-east, but none towards the south. Why 
should the drift current, after passing this ridge, suddenly turn towards the east and 
