Crosby.] 8 [January 16, 



1. It has long been a favorite notion with the geologists of 

 this region that the Roxbury puddingstone, if not all the con- 

 glomerate of the Boston basin, is of Carboniferous age. There is 

 no evidence supporting this view beyond the fact that the Car- 

 boniferous beds in the Narragansett basin are largely a distinct 

 conglomerate resembling that about Boston. Since the publica- 

 tion of my " Contributions," Mr. G. H. Barton and I have made a 

 careful study of the Carboniferous strata along the north side of 

 the Narragansett basin ; and we have proved by paleontologic 

 and stratigraphic evidence that the long narrow arm of this 

 basin reaching north easterly from Rhode Island to the Blue 

 Hills contains only Carboniferous sediments. This branch of the 

 great Carboniferous basin, which is called the Norfolk County 

 basin, terminates within one mile of the border of the Boston 

 basin, affording an excellent opportunity to compare the rocks 

 of the two basins. 



The Carboniferous shales and sandstones, except when distinctly 

 carbonaceous, are usually green or red, and are quite distinct 

 lithologically from the slates of the Boston basin. The conglom- 

 erates of the two basins are also noticeably unlike, the Boston 

 conglomerate being as a rule much stronger, much more thor- 

 oughly consolidated, and alternating less frequently with beds of 

 sandstone and slate. Both basins are bordered chiefly by erup- 

 tiue rocks, granite, felsite, diorite, diabase, etc., and in the case 

 of the Boston basin it is clear that the eruption of some of these 

 took place after the deposition of the conglomerate and slate. 

 But in the Carboniferous basin evidence of this kind is completely 

 wanting. Nowhere is there any indication that the granite or 

 other eruptive rocks forming the borders and probably the floor 

 of this basin reached their present positions subsequently to the 

 deposition of the Carboniferous sediments. For example, the 

 Blue Hill range of granite forms the southern border of the Bos- 

 ton basin and the northern border of the Norfolk County basin. 

 At most points where this granite meets the conglomerate and 

 slate of the Boston basin its relations to them is that of an exotic. 

 But on the southern side, where it adjoins the Carboniferous 

 strata, the relation is entirely different, all the granite being 

 clearly older than these sediments, proving that the latter belong 

 to a later period than the rocks of the Boston basin. Again, pre- 



