CHAPTER V. 



THE CARBONIFEROUS STRATA. 



DETERMINATION OF HORIZONS WITHIN THE BASIN. 



The earliest attempts to discriminate horizons within the limits of the 

 basin were made by Edward Hitchcock in the northwestern part of the 

 area, where, on lithological grounds, the red Carboniferous beds were 

 referred to the Devonian period. 



Sir Charles Ly ell, in 1 845, mapped as Devonian a broad band of strata 

 extending through Rehoboth, Swansea, Taunton, and thence to the eastern 

 margin, but it is now known that the beds so mapped are Carboniferous- 

 In 1871, C. H. Hitchcock mapped a small area in the southwestern part of 

 Attleboro as belonging to the "Quebec group," and a strip along the west- 

 ern border of Rhode Island as Silurian, but both these occurrences are now 

 known to be Carboniferous. In the earlier work of T. Nelson Dale about 

 Newport, the Carboniferous and earlier strata were divided into Paleozoic 

 groups based on lithological characters. Beyond these incomplete maps no 

 attempts have ever been made to exhibit the formations which have been 

 recognized by several authors as forming horizons in the coal basin. 



MEANS OF DETERMINING SUPERPOSITION. 



The means of determining horizons in the Carboniferous rocks of the 

 Narragansett Basin are purely physical. As yet the fauna and flora of 

 the Carboniferous beds are too little known to be employed. A series of 

 basal arkoses overlain or replaced from point to point by simple quartzose 

 conglomerates can be traced fairly continuously about the margin, and may 

 be recognized at a few points in the interior. Above these is a great 

 succession of conglomerates, sandstones, and shales with coal seams, which 

 are rarely traceable for more than a few miles. The formation is preemi- 

 nently conglomeratic. 



In the main, reliance has been placed on matching strata on opposite sides 

 of anticlinal and synclinal axes, checking these observations by gross meas- 

 urements of thickness and by observed gradations in texture and thickness of 

 individual beds. The results can be said to be little more than approxima- 

 tions. In portions of the area, particularly in the eastern part of the field, a 

 desci'iption of the geology can deal with little more than isolated outcrops. 



