﻿Gorge of the Farmington IZiver, Conn. 



431 



EAST GRAN-3?. 



BLOOMTIEU). 





range of trap hills, forming a most picturesque gorge, and beau- 

 tifully exposing the geological structure. The accompanying 

 map (on a scale of -jj-ths of an inch to the mile) shows the position 

 of the localities referred to. The let- 

 ter S indicates the location of the 

 Tariffville station of the Hartford 

 and Connecticut Western R. R. At 

 the point marked B, where the boun- 

 dary between the towns of Simsbury 

 and Bloomfield meets the river, the 

 river is crossed by a bridge. South- 

 ward the boundary between Sims- 

 bury and Bloomfield run§ along the 

 crest of the trap range. On the left 

 bank of the river, for some distance 

 above the bridge, rises a bold line of cliff about two hundred 

 and fifty feet in height, formed by the upper sheet of trap, which 

 here presents its usual characters, being highly columnar and 

 not amygdaloidal. Above the bridge, the sandstone appears at 

 the base of the cliff, forming for a considerable distance the 

 immediate bank of the river ; but, in the slight westerly bend 

 in the immediate vicinity of the bridge, the river has cut down 

 through the sandstone into the underlying amygdaloid. Start- 

 ing accordingly, from the bridge on the left bank of the river, 

 it is easy to examine the whole thickness of the strata from the 

 top of the lower (amygdaloidal) trap to the base of the upper 

 (columnar) trap. The thickness of the strata is apparently 

 about twenty feet, though it would require a little surveying 

 to determine the thickness with any degree of accuracy, as cov- 

 erings of talus and vegetation and the water of the river prevent 

 the whole thickness from being accessible at any oue point. 

 The rocks are more conveniently studied above the bridge 

 than below it, being less covered by vegetation. 



Starting from the margin of the stream at the bridge, and 

 proceeding upward until we reach the upper sheet of trap, we 

 may observe the following succession in the phenomena pre- 

 sented by the rocks : 



1. The greenish gray amygdaloid which forms the main part 

 of the lower sheet of trap. 



2. The same becoming less lustrous, less greenish in color, 

 and having the amygduies more copiously distributed, as we 

 approach its upper surface. 



3. A conglomerate, containing pebbles of amygdaloid. 

 Many of the pebbles show the rounded form of water-worn peb- 

 bles. Some of them show superficial alteration, such as is com- 

 mon in pebbles of trap exposed to the action of air and water. 

 The matrix in which the trap pebbles are imbedded, is the or- 



