636 GEOLOGY OF OLD HAMPSHIRE COUNTY. MASS. 



interesting. Long before reaching the Iwook it rises to the height of 318 

 feet and widens rapidly into a broad sand phiin, across whicli the Iwook, 

 emerging from the high lands at the road crossing near a magnificent 

 drumlin (called Belmont) that rises on the north a hundred feet above the 

 plain, runs, over a bed of coarse gravel which is very little lower than the 

 surrounding level, and at the front of the plain falls rapidly over a reef of 

 compact hornblendic granite (tonalite) into the valley below. Just south 

 this reef rises in a narrow ridge and runs parallel to and about half a mile 

 distant from the western rim of the valley, southward through Hattield, to 

 end in Elizabeth Rock in Northampton. At the highest water stand it was 

 a long island in the lake, or rather two islands, as it is broken through at 

 a point in the middle of its length, tlu-ough which the^" Running Gutter" 

 enters the main valley. Into this lateral valley the waters of West Brook 

 earned the greater part of the detritus they were bringing down, and the 

 plain we are following continues at the same high level, quite even and 

 sandy, for a mile farther south, bounded on the west by the steep, rockj^ 

 rim of the valley and on the east by this island; and from the south the 

 sands of the high bench in Northampton enter the side valley west of 

 Elizabeth Rock and pass up it for almost the same distance, while outside, 

 on the east of the rocky island which is called -'The Rocks," in Hatfield, 

 the fine sands of the broad lake bottom (1 b t) abut at a much lower level 

 directly against the bare clift's. 



On tlie shrinking of the flood ^A'aters West Brook found its way, not 

 down the western side trough into which nearly all its sands had been 

 can-ied, but, like so many other streams in the valley, by a detour to the 

 north around the north end of the granite ridge. In a similar way Broad 

 Brook, which heads in the broad sand plain north of Florence, runs a long- 

 way north up the trough we have just followed south, and breaks througli 

 "The Rocks" in the center of the ridge to join the main valley, searching 

 out for itself the most northerly outlet possible. 



This is sufficiently explained by supposing that the current of the 

 stream, combined with that of the main stream, kept the sands at a slighth' 

 lower level opposite its mouth than lower down, where they were spread 

 in the long trough of quieter waters, so that on the lowering of the water in 

 the main valley the tributary found its way through lower ground around to 

 the north of the bar; still, the many times this occurs in the valley, under 



