THE HOLYOKE SHEET, 447 



in Pelham, on Amethyst Brook. The sheet mouuts the hillside oliliquely 

 toward the west, and where it reaches the crest of the hill has a thickness 

 of about 260 feet, and where it crosses the first road, the Bay road, runnin<>- 

 to Belchertown, of about 370 feet. It presents only alow bluff to the north 

 and dips south with an angle of 25°. It does not grow nuich thicker as it 

 is followed west, nor does the bluff become more prominent until, havino- 

 passed the second road over the mountain, it rises to a much greater height 

 in the long, flat-topped ridge which is so marked an object as seen from the 

 north and which is locally called Long Mountain or Flat Top. The crest 

 has had across Belchertowxi a height of 450 to 475 feet above the sea, but 

 rises in Long Mountain to a height of 600 feet. This is explained in part 

 by the thickening of the bed, which measures here 542 feet east of the 

 Granby road, 612 feet at the eastern central, 770 feet at the center, and 824 

 feet at the western central part of the mountain. The last of these measm-e- 

 ments was made carefully with a chain by Mr. W. E. Sanderson. It would 

 seem that several undiscovered faults must have been crossed, as the number 

 seems nauch too large. 



This sudden elevation of Long Mountain is also partly explained by 

 the faults which bound it on the east and west and present the edge of 

 the sheet in this mountain' at a better ^angle for resisting the southward 

 movement of the ice. The fault on the east is beautifully marked, runs 

 with the dip, and transfers the outcrop of the bed southward by just the 

 amount of its width. The second fault is directed southwesterly, making a 

 large angle with the dip, and on its eastern side the dips have more easting, 

 so that the outcrop of the diabase extends southwestward for a long way 

 and ends in a point far south of the main ridge. (See PI. IX.) 



Following the ridge a mile west one sees a sharp, heavily wooded, 

 conical peak, locally called Rattlesnake Knob, which is the next marked 

 peak after leaving Long Mountain, and which is a quite exact imitation 

 on a small scale of the next high peak to the west, namely, Norwottock 

 or Hilliards Knob, the highest pcjint on the ridge east of the Connecticut. 

 To the east of the small cone is a deep, semicircular depression, exactly like 

 one at the western foot of Long Mountain, and like it caused by a great 

 fault. In both these depressions sandstone forms the crest of the ridge. 



Both these faults run southwest, and between them an isolated section 

 of the trap sheet, called Bishops Mountain, is placed, en Echelon, runnino- 



