GEOLOGY OF THE MERRIMACK DISTRICT. 521 



certain that we should not regard the Springfield gneiss as a part of the 

 porphyritic group. Lithologically, it is more like the Lake division. 

 Rarely crystals of feldspar are disseminated through it. The Montalban 

 section of rocks carrying coarse granitic veins is also cut off by this 

 Springfield gneiss. 



We have four or five sections crossing this porphyritic range. At the 

 north end, the formation is poorly exposed in Groton, on Cockermouth 

 brook, and the positions are represented upon Fig. 82, Plate XXL 

 The strata are said to dip about 30° E., in the fork of the road east 

 of Kimball hill. On the west the next ledges are of mica schist, dip- 

 ping 50° and 60° N. 40° W. Hence, there may exist a strongly marked 

 unconformity here. The rock through this valley in Groton contains 

 many fine-grained gneisses ; also, ferruginous schist west of A. Fox's and 

 the saw-mill, where the dip is 50° E. The rock is not seen in Hebron. 

 This section, therefore, makes the dip of this rock in Groton essentially 

 monoclinal. Farther north it is not seen, that is, for a distance of over 

 nine miles, when we come to the Moosilauke-Kinsman range. It is 

 probably exposed in the valley of Cockermouth brook, just at its northern 

 extremity. The country north rises rapidly, and constitutes a high ridge 

 about eight hundred feet above the porphyritic outcrops. This elevated 

 mass of rock is probably a later formation, occupying a natural depression 

 in the older rock. There may be an inverted anticlinal underneath the 

 Kimball hill schists, in order to enable the porphyritic rock to present a 

 proper face towards the easterly dipping gneisses of Dorchester. 



The next section traversed is from the north end of Crystal lake in 

 Enfield across Grafton and Danbury (Fig. 83). At the west end are strata 

 of the fine-grained Bethlehem gneiss, with easterly dips. On the east side 

 of East hill there is a gneiss somewhat porphyritic in aspect, dipping west. 

 The rock is like this for two miles into Grafton, but the dip has changed 

 to east. Then we pass the mica-bearing rock with its very coarse granite 

 veins, dipping 53° S. 20° E. and 70° S. 80° E. This rock is believed to 

 mark the place of a synclinal. The first ledges seen after leaving Grafton 

 Centre are of genuine porphyritic gneiss, but I have no observation 

 recording their position. The dips are believed to be easterly. In 

 Danbury there is a south-west dip near S. Howe's, a mile north-east of 

 the section. At the east end of the formation, half a mile north-west 



VOL. IL 66 



