646 STRATIGRAPHICAL GEOLOGY. 



Lake gneiss of Salisbury. The Montalban may extend a little beyond 

 Horseshoe pond ; after which are the close complicated axes of the Kear- 

 sarge group, illustrated in Fig. 103. Past Andover succeeds the great 

 central ridge of porphyritic gneiss in Wilmot, with two closely pressed 

 folds. Across Springfield and Grantham is the widest part of the Lake 

 gneiss development west of the central ridge to be found anywhere in 

 the state. There seems to have been an extensive uprising of the earth- 

 mass in this region, not sufficient to bring up the porphyritic rock, but 

 enough to prevent the deposition of the micaceous group, unless the 

 elevation took place after its accumulation, and its exposure to atmos- 

 pheric agencies has led to its removal by denudation. Portions of this 

 gneiss are somewhat porphyritic. There must be a synclinal between 

 Col. Sanborn hill and Station pond, both sides dipping easterly, the east 

 one the most. Stocker pond is about the place for the anticlinal. There 

 is a basin for the valley of Croydon branch in Grantham, on the west side 

 of which is a long stretch of white quartz. Farther west we come to an 

 area of Bethlehem gneiss, extending into Croydon, and possibly reaching 

 to the west border of the gneiss, though not so represented upon the map. 

 A synclinal to the east and an anticlinal on the west show us the struct- 

 ure of the area. Protogene gneiss characterizes the centre, and a por- 

 phyritic variety the west side of this development. The last dip is quite 

 moderate, only 15° W., and it is covered by the Coos rock of Croydon 

 mountain. The first met with is quartzite, dipping 75° N, W., and soon 

 afterwards the dip is in the opposite direction, so that the first range of 

 quartzite is a closely pressed basin. On the west slope of Croydon moun- 

 tain the mica schists with staurolite overlie the Calciferous schists, proba- 

 bly by inversion. The attitude of the rocks through Cornish is expressed 

 in Fig. 62, page 397. This is the broadest area of this formation in the 

 state, and is evidently characteristic of the group. The eastern portion 

 is clearly monoclinal, and here is inverted. Two or three faults develop 

 subordinate axes in the west part of the town, the first between two Hu- 

 ronian bunches, the second occurring on the east bank of the Connecti- 

 cut, a short distance above the bridge. These Huronian bands are the 

 narrow representatives of hornblende and hydro-mica schists developed 

 much more extensively farther north. Crossing into Windsor the section 

 passes over Mt. Ascutney, which is a high mountain composed of igneous 



