336 



STRATIGRAPHICAL GEOLOGY. 



saw-mill and perhaps Fitch hill. The other strata belong to the Swift 

 Water division of the Huronian. There is a resemblance between the 

 mica schist spoken of and the rock of Eustis hill. The gneiss following 

 belongs to the Bethlehem group, dipping 30° northerly, and is a part of 

 the range mentioned upon page 274, running into Bethlehem, and termi- 

 nating less than two miles south-west from the section line. Whatever 

 may be the stratigraphical character of this group in Bethlehem, it* is 

 practically an inverted anticlinal at North Lisbon, since it is flanked on 

 both sides by newer rocks, all dipping in the same general direction, un- 

 less the discordance in strike of the gneiss and Huronian is of enough 

 consequence to be styled an unconformity. 



Fig. 43, if protracted, would cross another interesting Helderberg area; 

 but, for the sake of clearness, I will add a small section (Fig. 44), with 

 greater horizontal scale, situated about a quarter of a mile to the south- 

 i g west, crossing the Ammonoosuc nearly at North Lisbon 

 "^ ;3 railroad station, and passing up its south branch. The 

 I Z gneiss dips 36° N, 47° W, at the lead mine. Next is a 

 X S coarse conglomerate, seen in the field and under the 

 >^ "^1 bridge, dipping 6s°-70° N. 22° W. As there is a gen- 

 # i J eral resemblance between this and the conglomerate of 

 s' I = the Lisbon group, it was not till the recent discovery of 

 h5 I extensive Helderberg strata that these ledges at North 

 I * & Lisbon appeared to belong to the Paleozoic series. The 

 J I 3 materials of the pebbles are white and blue quartz, hy- 

 " '^ ^ dro-mica schist or Lisbon group, two or three gneisses, 

 I I o Coos slates, and calcareous masses, with an argillo-mica- 

 ceous paste. Some pebbles are a foot long. They are 

 usually slaty, but not contorted. 



Crossing the river and walking over twenty rods of gravel, we came 

 next to a more interesting locality in the South Branch valley. The first 

 ledge, back of the last house on the road, is micaceous slate, with calca- 

 reous layers, cut by an obscure igneous dyke. The strata dip 45° N. 32° 

 W. Beneath are fifty feet of coarse conglomerate, containing, in addi- 

 tion to the pebbles under the bridge, pieces of the mica schist of the 

 Coos group, without staurolite. The slates next observed have a higher 

 dip. They are followed by indurated slates dipping 50° N. 22° W. They 



