GEOLOGY OF THE MERRIMACK DISTRICT. 497 



the corner of the town. The easterly band does not extend much south 

 of the north end of Newfound lake, but eastward it is the rock of 

 Plymouth mountain, where the rock contains fibrolite. East of A. J. 

 McClure's, and at the town-house, we have fine-grained granitic gneiss. 

 In the south part of Groton, between the two bands of fibrolite schist, we 

 have coarse gneisses, sometimes porphyritic. The westerly band of 

 schist that extends south-west from North Groton, outcrops in extensive 

 ledges near where the road crosses Cockermouth brook, and it extends 

 west into the edge of Dorchester. South of Kimball hill, and at G. 

 Thompson's, the rock resembles the more micaceous of the Montalban 

 series. Coarse granite veins are quite common in Groton and Hebron, 

 and some of these carry fine crystals of beryl and mica. In the narrow 

 band of fibrolite rocks in the south-west part of Groton we no longer find 

 the synclinal structure that we saw in the broader band northward, but 

 all the rocks have an easterly dip. Section VI crosses the south part of 

 Groton, and the dip of the rocks will be given, which will show the rela- 

 tion of the fibrolite schist to gneiss. 



In Orange, a line drawn from near R. R. Smith's south to Grafton, 

 passing near the outlet of Orange pond, will point out the boundary 

 between the fibrolite schist and the porphyritic gneiss. Another line, 

 drawn from near the north-west corner of Orange, and bending to the 

 west so as to pass just through the border of Canaan, near W, Davis's, 

 turning eastward to the forks of the road near S. H. Stevens's in Orange, 

 thence southward to a point between the height of land and Tewksbury 

 pond, will follow nearly the western boundary of the fibrolite schist. 

 Here, as southward, we have the Lake gneiss on the west. It will be 

 noticed that the schist is quite variable in width, being two miles and 

 three quarters in width on the north, and for some distance southward, 

 when it suddenly contracts, near the middle of the town, to a band a mile 

 and a half in width ; and on the southern border of the town it is not 

 more than a mile wide. In this area most of the strata are nearly verti- 

 cal, and in the narrower portions it has both an easterly and westerly dip. 

 There are coarse granitic veins in several places, and fibrolite can gen- 

 erally be found. 



In Grafton the band widens somewhat, and here we have the coarse 

 granitic veins that have produced so much mica. The rock can be seen 

 VOL. IL 6^ 



