1884.] 9 [Crosby. 



ceding, during and following the deposition of the conglomerate 

 in the Boston basin there were extensive outflows of basic lavas, 

 now commonly known as amygdaloid, which are believed to be 

 entirely wanting in the Carboniferous basin. 



Finally, the conglomerate and slate of the Boston basin are 

 traversed in all directions by numerous and large dikes of trap 

 or diabase, so that it is rather exceptional to find large exposure s 

 of either of these rocks which do not show one or more dikes. 

 Some of these dikes are from one to several hundreds of feet in 

 width and several miles at least in length ; and there can be but 

 little doubt that many of the dikes cutting the crystalline rocks 

 outside of the Boston basin are of the same age. Now, if the 

 Boston conglomerate is Carboniferous then these dikes must be 

 post-Carboniferous ; and it is in the highest degree improbable 

 that this immense volcanic activity, which has made the Boston 

 basin a complete network of dikes, would not be felt in some 

 degree at least in the adjacent Norfolk County basin, the shortest 

 distance between them not exceeding one mile. But Mr. Barton 

 and I have examined every ledge in the Norfolk County basin, 

 and in the adjacent portions of the Narragansett basin, without 

 finding a single dike or any trace whatever of any eruptive rock 

 newer than the Carboniferous beds. Excepting possibly one very 

 small dike in the neighborhood of Canton. And Mr. T. Nelson 

 Dale,^who has made a careful study of the Carboniferous beds in 

 the vicinity of Newport, tells me that there appears to be a com- 

 plete absence of eruptive rocks in that part of the Carboniferous 

 basin. 



To sum up, although in both basins the rocks are strongly 

 folded and have high dips, yet in the Boston basin all the rocks, 

 including the conglomerate, are distinctly more consolidated and 

 older looking; and preceding, during and following their deposi- 

 tion this basin, including probably the surrounding region, was 

 the scene of the most intense volcanic action, while no eruptive 

 rocks have ever been discovered in the adjacent portion of the 

 Carboniferous basin. In the complete absence of paleontological 

 evidence pointing to a contrary conclusion, these facts certainly 

 require us to believe that all the sediments of the Boston basin 

 are pre-Carboniferous. 



2. I have never observed in either the slate or the conglomer- 



