BOUNDARY OF THE BASIN. 127 



From the Blackstone River to Sheldonville. ThrOUgllOllt tlllS n01'tliei - Il half of tlie 



western boundary actual contacts of the Carboniferous upon the underlying 

 rocks have not been seen. North of the Blackstone River the NW.-SE. 

 strikes of the Blackstone series can be traced to within short distances of 

 the NE.-SW. strikes of the Carboniferous beds, indicating from the angle 

 which the latter make with the western boundary that they have probably 

 been faulted. From Millers River northward a boundary valley continues 

 as far as Diamond Hill. In the Millers River section gray basal conglomer- 

 ates dip off eastward at steep angles, but the valley is wholly excavated 

 in the Carboniferous rocks. Northward, in the Thompsons Hill area, the 

 Coal Measures come in, apparently by dowufaulting along the border. 

 From Diamond Hill to Joes Rock, seen on the Franklin atlas sheet, the 

 Carboniferous rocks are in unconformable relation with the lower Cam- 

 brian red shales, but details of this relation are wanting. 



Connection between the Narragansett and Norfolk County basins. At Slieldoilville the TOCk 



of the Narragansett Basin can be traced, as stated by Crosby and Barton 

 in 1880, into the southwestern end of the Norfolk County Basin, through 

 a pass not exceeding 2,500 feet in width between walls of the hornblende- 

 granitite. The hornblende-granitite comes up to this stratigraphic isthmus 

 with nearly rectangular corners, as shown in the map, fig. 7 (p. 12 1). 1 



sheidonviiie cross fault. — The most reasonable explanation of the rectangular 

 boundaries of the Carboniferous and granitic rocks at this point is, as sug- 

 gested by Mr. J. R. Finlay, the occurrence of a fault passing in a NNW.- 

 SSE. direction. This view is confirmed by the extensive faulting of the 

 Carboniferous beds southward through Plainville in the same direction, as 

 Mr. Finlay has amply demonstrated in the field. 



Actual fault contacts in the Sheldonville pass have not been seen. 

 There is an outcrop of red sandstone striking NE. and dipping 60° N. in 

 the pass in the western granitic corner, very close to the supposed fracture. 



From sheidonviiie to Foolish Hiii. — From near Burnt Swamp Corner eastward the 

 boundary can be fixed with approximate exactness. Messrs. L. S. Griswold 

 and C. F. Marbut have determined the relations of the rocks at a number 



1 Some of the earlier geologists supposed that the Rhode Island and Worcester areas are con- 

 nected through the Blackstone Valley, but Prof. Edward Hitchcock showed that these areas are 

 separated by a wide district of gneiss. Dana, Manual of Geology, 3d ed., 1880, p. 319. Hitchcock, 

 Final Report on Geology of Massachusetts, 1841. 



