424 



Scientific Geoldgy. 



Not improbably also, the elevating force, which has acted on the side 

 of the gneiss and granite, may have operated in wheeling these cen- 

 tral strata still farther, so as to bring their direction nearly east and 

 west. 



In another place I shall refer to the important bearing which this 

 section has upon the the theory of the origin of our greenstone : but 

 in this place I wish to show more particularly the relative situation of 

 the greenstone and sandstone. It will be seen that the former occurs 

 in somewhat wedge-shaped masses, between the strata of the latter, and 

 I believe that the above section represents the mode in which nearly all 

 the greenstone in the Connecticut valley occurs. On the western slope 

 of Mount Toby, in Sunderland, we find a narrow strip of the green- 

 stone interposed between the sandstone strata ; although I cannot say 

 that it is wedge-shaped ; the opportunities for ascertaining, the dip 

 being very poor. Along the western and northwestern face of Mount 

 Holyoke, however, we meet with the sandstone in several places, (al- 

 though not very easy to find,) passing under the greenstone with a 

 dip of 15° or 20°. On the opposite side of the mountain the strata are 

 sometimes found elevated 50° and even 60°; as may be seen where the 

 stage road from Northampton to Belchertown crosses the greenstone 

 ridge ; and as we recede from this ridge, towards the east, or south- 

 east, the dip diminishes. In the west face of Mount Tom, we find the 

 sandstone passing under the greenstone at a dip from 15° to 20° : but on 

 the east side of the mountain, it is no greater ; and, therefore, I cannot 

 say that this eminence has a wedge-shaped form. South of Tom the 

 sandstone both on the east and west sides of the greenstone ridge, 

 has a less dip then in the cases above mentioned. Still, however, 

 the greenstone seems to form a mass interposed between its strata. 



Are we to regard the long ridge of greenstone extending from 

 New Haven to Belchertown, as a vast dyke, or as a bed, or simply 

 as a protruding irregular mass 1 Its great length, (though not 

 greater than the celebrated Cleaveland dyke in England,) and espe- 

 cially its great width in some places, will hardly permit us to call it 

 a dyke, as geologists usually employ that term. A still stronger ob- 

 jection in the minds of many, would be its general conformity in di- 

 rection to the strata of sandstone. But near its northern extremity, 

 it is obvious that this conformity is in a good measure lost. For 

 Holyoke, running nearly east and west, evidently crosses the strata 

 in some degree : or rather, these same strata which farther south 

 have their western edges elevated by the greenstone, on the southern 



