10 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



and simple character which mark its more northern course. Tlie crystal- 

 line rocks are tlien set back 7 miles to the west, along the northern border 

 of Greenfield, and the rocky boundary thence goes south, with sharp east- 

 ward slope, notched only by the Deerfield gorge, to be again set back by 

 about the same amount along the north of Northampton. It then runs 

 south again, interrupted only by the Westfield River, to and beyond the 

 south line of the State. 



On both sides the brooks and the roads (which usually follow the 

 brooks) come down sharply from the uplands, and railroads can enter and 

 leave the valley only by the four tributaries mentioned above. 



Just south of where the western boundary first turns westward, in 

 Greenfield, a great block of red sandstone hills, occupying the whole town 

 of Gill, separates the valley into two parts, the river occupying the eastern 

 portion and the narrow, high Bernardston Pass connecting it with the north 

 end of the western portion. From the southwest comer of this mass the 

 Deerfield trap sheet runs southward, forming Deerfield Mountain, its ver- 

 tical western scarp making the eastern boundary of the Avestern lateral 

 valley, which preserves its width southwardly through Deei-field, while east 

 of it the valley of the Connecticut proper expands into the Montague basin, 

 the ridge being much narrower than the block of liills in Gill, which makes 

 the northern border of this basin. On the south the great mass of Mount 

 Toby shuts in this Montague basin, the river passing in a narrow valley 

 between it and the south end of the Deerfield range, which ends abniptly 

 with Sugar Loaf, into the much broader Hadley basin, while a deep, nar- 

 row valley around the east side of Mount Toby also connects the two. 

 Bv the breaking down of the Deerfield range the Deerfeld Valley opens 

 widely into the Inroad Hadley basin, which here has the full M^dth of the 

 Connecticut Valley, 1 4 miles, between the crystalline borders on the east 

 and west, though Mount Warner, a mass of crystalline rocks, stands mid- 

 way to partly continue the barrier. 



South of Amherst the Holyoke range rises abruptly athwart the valley, 

 leaving a narrow passage on the east into the Springfield basin, like that 

 around the east end of Mount Toby, while it is broken through for the 

 escape of the river just as the latter comes through a narrow passage 

 between Mount Toby and Sugar Loaf on its entrance to the basin. 



Tlie Holvoke range extends south along the western border of the 



