GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT. 36/ 



80° S. 70° W., also standing on edge, seem to be a repetition of this 

 band, — perhaps the eastern border of the principal area. (See Fig. 6i.) 

 In agreement with our theory of the relative ages of the rocks about 

 Hanover, we have the repetition of the hornblende rock on the east side 

 of the Bethlehem gneiss, in the central parts of the town, midway be- 

 tween Hanover centre and Mill Village. The general situation of the 

 formation along the river is in the line between the Bethlehem group and 

 the Huronian, with a westerly dip. Inasmuch as a rock of similar min- 

 eral character is associated with the Coos slates, the first supposition 

 placed the two together as a part of the newer group. Reflection sug- 

 gests that it should be regarded as an older member than the Coos, pos- 

 sibly even underlying the Huronian. Further descriptions will set forth 

 interesting ranges of hornblende overlying other areas of the Bethlehem 

 group in Grafton and Cheshire counties, which stand related to the anti- 

 clinal ridge extending from West Brattleborough to Leyden, Mass., at 

 Shelburne Falls, Mass., and elsewhere in southern Vermont. They seem 

 to be more nearly allied to the Huronian than any other system of strata. 

 It is probable that these schists in Piermont should be referred to the 

 same age, though for convenience described with the Coos slates farther 

 along. A limited outlier of the same rock in Cornish will be noticed in 

 the description of Section V. 



Cambrian. 



Allusion has been made (p. 311) to the existence of three ranges of 

 clay slate along the Connecticut valley, — first, the more northern one 

 from Kirby to Barnet in Vermont; second, the series of basins in the 

 Ammonoosuc gold field ; and third, the larger area from Fairlee to Hart- 

 land in Vermont, repeated again below Ascutney from Rockingham to 

 Massachusetts. Extensive argillaceous and slaty rocks occur on the east 

 side of the river, and upon previous maps I have colored them the same 

 with these Vermont ranges. With the exception of the one extending 

 from Plainfield to Charlestown, upon the east side of the calciferous mica 

 schist, I think the latter should be placed with the Coos group, since they 

 often contain staurolite, and especially a multitude of garnets. It is very 

 uncommon to find these minerals in the former set of ranges, so that for 

 the present I think it desirable to separate these argillaceous develop- 

 ments from each other, calling the one Cambrian and the other Coos. 



