534 



Scientific Geology. 



connected with this system, by which to judge of the epoch of its el- 

 evation. We could learn here only that it took place after the depo- 

 sition of the graywacke. But according to Beaumont, it took place 

 between the deposition of the chalk, and the oldest of the tertiary 

 strata. 



5. East and West System. 



This includes the greater part of the graywacke, granite, sienite 

 porphyry, and greenstone, in the eastern part of the State ; and prob- 

 ably the gneiss in the vicinity of New Bedford. Amid many anom- 

 alies, the decidedly predominant direction of the strata of graywacke 

 (excepting the portions connected with the last system,) is east and 

 west, and the dip notherly. Not having made many observations up- 

 on the New Bedford gneiss, and finding that sometimes its strata 

 tend northeaster!}'- and southwesterly, I was at first inclined to refer it 

 to the last described system. But more probably I think, it should be 

 connected with the system under consideration. 



So limited is the graywacke in some portions of the region embrac- 

 ed by this system, as I have stated its boundaries, that it would be de- 

 sirable to find other evidence that the granite, sienite,porphyry, and 

 greenstone, along the eastern part of the state, belong to the same sys- 

 tem of elevation. And fortunately this evidence is presented in the 

 east and west direction of nearly all the mountain ridges and chains of 

 hills composed of these rocks. The most striking example of this 

 fact is the Blue Hills, made up of sienite and porphyry, and forming 

 the most elevated land in the eastern part of the State. The porphyry 

 range a little north of Boston has the same general direction ; and so 

 have many smaller ridges to the south of the Blue Hills. In Sharon, 

 Foxborough &c, however, the sienite ridges assume a direction near- 

 ly northeast and southwest, or somewhat nearer to the meridian than 

 this. This is the case with the Moose Hill range, for instance, which 

 is more than 400 feet high, and runs northeast and southwest: and 

 this, with other parallel ridges in that vicinity, obviously belong to 

 the last system of elevation that has been described.* And this is 

 what we might expect, since a portion of the graywacke running 

 through Walpole and Wrentham, and belonging to the northeast and 

 southwest system, occupies the vallies between these ridges. 



I have suggested in another place, that the disturbance which the 



*H. E. Rogers in the Report on the Providence and Boston Rail Road, p. 59 and 

 61. 



