Geology, <^c. of the Connecticut. 51 



wacke* may be found lying between the greenstone and the 

 sandstone, as at Gallows-Hill near Hartford, and on the 

 west side of the Berlin ranges of greenstone. Some of the 

 greenstone occurring in the dykes of this rock in old red 

 sandstone, has a similar aspect. At the junction of the 

 coal formation and greenstone below the falls in Gill, the 

 columnar tendency of the latter rock entirely disappears, 

 and for several feet, the greenstone is distinctly, though 

 somewhat irregularly, stratified; the strata being parallel 

 to the sandstone. This may be seen to most advantage at 

 very low water; and the same maybe seen, though less 

 distinctly, along the whole eastern border of this range of 

 greenstone ; and something of it on the east side of all the 

 greenstone ranges along the Connecticut. It ought here 

 to be remarked, also, that this rock appears quite diiferent 

 in its composition on the eastern side, especially of the 

 range passing through Deerfield and Greenfield. The in- 

 durated clay seems in a great measure to take the place of 

 the hornblende, and the basis of the rock has a wacke-like 

 appearance. Much of it is amygdaloidal; but the imbed- 

 ded minerals are usually quite different. On the east side, 

 the most abundant is chlorite, having a radiated aspect, and 

 green earth ; whereas, on the west side, this is scarcely to 

 be found. The radiated zeolite on the west side is finely 

 fibrous; on the east side, the crystals are larger and trans- 

 parent, resembling the Thomsonite of Dumbarton in Scot- 

 land. The rock on the eastern side is, also, more decom- 

 posable than on the opposite side. 



The eastern side of this rock is not, however, all amyg- 

 daloidal. Near where Deerfield river passes through the 

 range, on the north bank, this rock contains distinct crys- 

 tals, or rather plates of felspar; and thus becomes a porphj- 

 ritic greenstone. "It even approaches to ophites,'' says 

 Professor Dewey. The same rock contains good prehnite, 

 and in the prehnite may be found pyritous copper. 



I should judge that about one half of the greenstone of 

 the Connecticut constitutes the base of amygdaloid, and 

 very much of it appears to be genuine toadstone. The cavi- 

 ties are usually spheroidal or almond shaped, sometimes 

 reniform, and frequently cylindric. Those of the latter 



*I have recently found xvacke perfectly well characterised, and very 

 abundant, at the foot of the very lofty mural precipices, two miles north 

 of Monte Video, on the Talcot mountain, ten miles W. of Hartford.— £rftVor 



