3/0 STRATIGRAPHICAL GEOLOGY, 



etc. I suppose the formation marks a horizon between the Huronian and 

 Calciferous mica schist. 



The quartz veins of Thetford are auriferous, and resemble those of Ly- 

 man, The galena is more abundant in the former locality ; and the other 

 characteristic minerals, as ankerite, blende, and mispickel, are present. 

 Quartz veins occur also in Norwich and Hartford; and in the latter town 

 there is said to be a gold-mining location. 



There is another range of clay slate connecting our two areas of de- 

 scription, to the east of the Connecticut and the Calciferous, from south- 

 ern Plainfield to North Charlestown. It bears the same relation to the 

 Cornish and Plainfield area of Calciferous mica schist that the Thetford 

 range just described does to the great Calciferous range to the west. In 

 Plainfield the ledges lie a short distance east of the school-house No. i6. 

 Many of the exposures in the east part of Cornish resemble this series ; 

 and on the west slope of Croydon mountain, opposite Parsonage hill, 

 there is a quarry of slate, the flags dipping 60° S. 80° E. Their exten- 

 sion southward is noted as argillaceous in the deep valley of a small 

 stream between N, Lear's and Mrs. Huggins's, and their position is sim- 

 ilar to that just noted. In Claremont the slates are much better devel- 

 oped. There is a small quarry on Redwater brook, in the north edge of 

 the town ; and Bald mountain is mainly composed of this rock, with in- 

 tercalated sandstones and quartzites. Between Bald and Green moun- 

 tains, on the "cat hole road," there are clay slates dipping 40° E. They 

 occur at intervals on the road following around the west and south flanks 

 of Green mountain, dipping S, ^y" E, very near the junction of the slate 

 with quartzite. In the valley of Sugar river, towards the village of Clare- 

 mont, the ledges show evident marks of distortion, with average, dips of 

 70° S, 85°-87° E. They are also permeated by many fissures, produced 

 in comparatively modern times, since they are not filled by veins. At 

 Mrs. O. Walker's there is a dip of 6y° N. 70° W,, which may be of limited 

 extent. Farther east there is another small synclinal, the basin being not 

 more than fifty feet wide. Of this the westerly dip on the east side is 

 very steep, while the easterly dip on the west side is not over thirty de- 

 grees. At the end of this side road, by S. Nott's, the dips are mostly to 

 the east, with the strike N. 30° E. Nearly opposite, on the main river 

 road, we find a strike N. 7° W,, and easterly dip. Near H, Hubbard's 



