GEOLOGY OF THE MERRIMACK DISTRICT. 467 



and generally carrying fibrolite, — is the rock of some of the highest 

 mountains in this district. East of Baker's river we have Mt. Carr and 

 the ridge extending southward, that terminates so abruptly in Rattlesnake 

 mountain west of Rumney. Southward we have high hills and moun- 

 tains : Plymouth mountain, in Plymouth ; Mt. Crosby, in Hebron, from 

 the summit of which we have such a fine view of Newfound lake ; Tenney 

 hill, immediately north, and the high land in Groton ; then we have, south, 

 the deep valley of Cockermouth brook, and the high hills between this 

 and the north-east branches of Mascomy river, and south of these the 

 porphyritic gneiss of Mt. Cardigan. The water-shed then descends to 

 the famous notch in Orange cut by the Northern Railroad. In Grafton, 

 the country everywhere is high ; Isinglass hill, Alger's hill, where the 

 immense beryls are found, Ford hill, a little south-west of the last, and 

 Prescott hill, are the most noticeable points ; — they vary in height from 

 1600 to 1800 feet. The ridge which we have followed, if it appears in 

 Springfield, except in the extreme northern part, is not prominent above 

 the general level of the country. It appears, however, again southward, 

 in a high ridge in the east part of Goshen ; also, in Lempster mountain, 

 and still farther south in Surry mountain. The country in the south-east 

 part of Cheshire county and along its southern border is everywhere high 

 land, having an average of at least a thousand feet above sea-level. Well 

 marked hills are not very numerous ; hence Monadnock is one of the 

 most prominent mountains in the state, as the view in every direction is 

 unobstructed. In the east part of Winchester, in the west part of Rich- 

 mond, thence northward in Swanzey and extending into Keene, are round 

 hills and mountains composed cheifly of gneiss. The depression in this 

 area seems to have the general direction of north-west and south-east, 

 though there are others not so well marked in other directions. It is to 

 be noted, however, that they pass through nearly all the varieties of rock. 

 The following are the prominent groups of rocks noticed, in what appears 

 to be their order of superposition, beginning with the lowest : 



1. Porphyritic Gneiss, for the most part, forms the eastern boundary of 

 the area we propose to describe; but it has outliers in the south which 

 extend to the western part of the district. 



2. Bethlehem or Protogene Gneiss. This rock varies somewhat in tex- 

 ture and composition in this area. That in Enfield is very closely allied 



