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° £., to be straight, and to be four miles long. This ridge was an ui^lift, 

 sloping towards the west, and presenting its broken and precipitous face towards the 

 east. It is 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 striae 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 strise was noted there as 5° east of north. So, 

 too, following along the north-east spur, there is no change in the striae 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 striae 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 strice 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 striae 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 strias. On the 

 contrary, there is every facility for the drift current after passing this ridge to continue 

 on in a 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 cast and 



