THE NATIONAL INSTITUTION. 197 



COMMUNICATED BY S. WEBBER, M. D. 



Sketch of the great Geological Features of the Valley of Connecticut River, at 



Charlestown, Neui.Hampshire, and Remarks on some Crystals found in the 



Slate-rock scattered in that region ; with specimens. 



The valley of the Connecticut river, in its widest extent, may be said to be in. 

 eluded between the summits of the Green Mountains of Vermont on the west, and 

 those of the granite ridgo, forming the height of land between it and the valley of 

 the Merrimac, on the east. From the edges of the proper valley in which its waters 

 flow, there is a continual though broken rise to these great boundaries, from whose 

 sides flow the tributary streams of the river. The immediate valley is bounded by 

 a steep ridge of hills on either side, between the feet of wliich and the river spreads 

 an extent of fertile meadow ; the deposit of the river, through which it winds its way, 

 alternately approaching to and receding from tliese ranges of hills. The nucleus and 

 substance of tliese hills in Charlestown, consists of strata of argillaceous slate, up. 

 turned nearly perpendicularly, the direction of the strata being nearly north and 

 south, and the dip a little to the south of east. On the east side, passing over the 

 summit of this first ridge, there is a slight valley, beyond which rises a ridge of 

 granitic structure, seeming as if forced up through the chasm made by the depres- 

 sion of the eastern edge of the slate strata forming the first ridge, and holding them 

 in place by its pressure on the inverted edge and sloping surface. Somewhat the 

 Jiamc arrangement is to be found on the western side. The following is a sketch : 



A 



n I Strata of slate. 



C C. Granite ridges. 



d d. Earth and coarse gravel forming the outer surface of the hills, in many 

 places stratified, and resembling the deposits in the bed of a river. 



e e. Meadows or interval land, consisting of fine silt. 



G-. River. 



g. Plain of fine yellow sand, with a slight covering of vegetable mould, upon 

 which stands 



/. The village of Charlestown. 



The arrangement is not, however, altogether so simple as is represented in this 

 sketch. The granite is often intermixed with bods of gneiss, many of them up- 

 turned like the strata of slate, and running parallel to them. These, as well as the 

 slate, arc seamed with veins of fiuartz, and sometimes of calcareous spar ; and there 

 arc all gradations of slaty structure, from gneiss to argillaceous slate. In some 

 places the slate is wanting, and the granite approaches close to the river, and even 

 extends into it. On the Vermont side, bods of limostoiio occur occasionally be. 

 twcen the slate and tlic granitic rocks. 



