416 



Scientific Geology. 



mont and New Hampshire in this valley, greenstone occurs in con- 

 nection with argillaceous and mica slate : but probably this is a vari- 

 ety of hornblende slate. The greenstone which I am now describing, 

 is associated with the new red sandstone: and ridges of it may be seen 

 extending almost uninterruptedly from New Haven, Ct. to the north 

 line of Massachusetts. The principal ridge commences with West 

 Rock, at New Haven, and extends from thence, almost in a right line, 

 to Mount Tom in Massachusetts. In Connecticut several other ridges 

 and hummocks of this rock exist to the east of this principal one ; 

 as may be seen on a geological map of the Connecticut valley, which 

 I prepared for the 6th volume of the American Journal of Science. 



The principal greenstone ridge above noticed, crosses the Connec- 

 ticut river between Holyoke and Tom, and curving towards the east, 

 terminates in the north-west part of Belchertown. At the southern 

 extremity of Mount Toby, however, we meet with another much 

 more diminutive ridge, or dike of this rock, which almost coincides 

 in direction with the meridian through Sunderland, and cross- 

 ing Connecticut river near the north line of that town, rises in 

 Deerfield to a much greater altitude, forming the eastern half of that 

 range of hills which occupies the eastern part of that town and Green- 

 field. In Deerfield the eastern side of the greenstone is very gentle 

 in its slope, and precipitous on its west side. But in Greenfield, al- 

 though the western side continues to present a mural face, its eastern 

 side also is very steep; being washed by the waters of the Connecti- 

 cut. This ridge terminates at Turner's Falls in Greenfield. Anoth- 

 er parallel ridge commences at the same place, only a few rods distant 

 but on the opposite side of a small river, (Fall river,) in Gill, and ex- 

 tends more than a mile towards the center of that town. Beyond the 

 extremity of this ridge, I have not found any greenstone except that 

 which I have described as a member of the hornblende slate forma- 

 tion. A deposit of this, as may be seen by the map, commences, in 

 the north part of Gill, only three or four miles north of the point 

 where the greenstone already described terminates. 



The external aspect of the greenstone in the Connecticut valley, 

 is very different from that of the same rock in the eastern part of the 

 State. Much of the latter is of a dark color, or when examined near- 

 er, of a green aspect, from the presence of epidote. But the former 

 almost universally exhibits a gray or iron rust color, either from in- 

 cipient decomposition, or from the presence of oxide of iron. 



The most common variety of the greenstone in the Connecticut 



