412 GEOLOGY OF OLD HAMPSHIKE COUNTY, MASS. 



dikes from a half inch to an inch across, which are at times abundant in the 

 gneiss, they reach a degree of fineness never seen in the central dikes, and are 

 in part or wholly made up of glass, and contain olivine, which allies them to 

 the newer outflows in the main valley. 



1. The most northerly of these dikes cuts g-neissoid rocks on the east 

 bank of the Connecticut, a few rods below the mouth of Millers River. The 

 dike is about 3 feet wide and runs south from the water's edge and disap- 

 pears in a short distance beneath the terrace sands. It is a compact, very 

 fresh, dark-gray rock, with few porphyritic feldspars I'^^'long and extinc- 

 tion 21° on either side of the twinning suture, the smaller feldspar 0.12™™, 

 the light-yellow augite peculiarly gramxlar and without crystalline outline. 

 Magnetite is very abundant. This occurrence is cited by President Hitch- 

 cock in his first report,^ and incorrectly assigned to Erving in the Final 

 Report.'- 



2. The next dike is intruded along the bedding of the gneiss, in the 

 vertical wall which forms the north bank of Millers River, east of the bridge 

 in the village of Millers Falls. As the gneiss has a low dip to the west, 

 the dike, which is about 7 feet wide, reaches the water's edge just west 

 of the Ijridge, where its crossing the stream gave rise to the falls from 

 which the village gets its name. The rock was not distinguishable in thin 

 sections from that of the preceding occurrence. 



3. The next outcrop was a knob of remarkably fresh ice-worn rock 

 exjiosed in the cutting made in 1881 in the relocation of the railroad tracks 

 a few rods south of the Millers Falls station. The diabase was exposed 

 in a rounded ice- worn boss, 10 or 12 feet across, without contacts. A few 

 yards to the east, and 2 yards lower, gneiss was exposed, in which rock 

 the diabase was dovibtless intruded. 



4. President Hitchcock notes greenstone in Montague, on the west 

 border of gneiss, 2 miles northeast of the meetinghouse. It separates in 

 plates directed east and west and standing vertical.' This locality is beside 

 the railroad, a mile south of Millers Falls, south of J. Hannegan's house. 

 A ridge 325 feet long, 82 feet wide, and 20-30 feet high runs N. 35° E., 

 surrounded by the terrace sands. The last three outcrops may form parts 

 of one long dike. 



iQeol. of Mass., 1835, p. 417. 



•Ibid., 1841, p. 648. 



»Geol. Mass., Final Report, 1841, p. 648. 



