36 GEOLOGY OF THE l^ARKAGANSETT BASIN 



their present position from the original strata b}^ the action of the last ice 

 period. Forming, as they do, a considerable part of the mass of conglom- 

 erates in the Narragansett Basin, it is clear that they were derived from an 

 extensive field. Their condition indicates that they were imported from 

 that field by torrent action. Although it is possible that these qnartzite 

 deposits originally lay over the country to the westward of the Narragansett 

 Basin, the failure of the beds to appear round the periphery of that area 

 leads to the supposition that the district whence they were derived lay to 

 the eastward of the trough, perhaps beneath the region now covered by the 

 sea This supposition receives some warrant from the fact that these peb- 

 bles are most abundant in the eastern portion of the basin, while they seem 

 to be almost lacking in the western part The existence of these pebbles 

 well toward the extremity of Cape Cod appears to indicate the occurrence 

 of similar deposits beneath the waters of Massachusetts Bay. For further 

 details concerning the origin of these qnartzite pebbles, see Fart II, by 

 Mr. Woodworth. 



AGE OF THE CAKBONIFEr.OUS ROCKS OF THE BASIK. 



The evidence goes to show that from the earliest stages of the Pale- 

 ozoic to the beginning of the era when the Carboniferous beds of this 

 district began to be laid down the field was mainly, if not altogether, the 

 seat of erosive actions. No remnants of the formations between the lower 

 Cambrian and the Carboniferous have been foimd in folds which exist in 

 the basement rocks of this part of the country. The fact that beds of 

 Cambrian age have survived at several points in the Narragansett Basin in 

 the region to the northward, while no deposits of the Silurian or Devonian 

 horizons have been identified, leads to the supposition that the sediment- 

 making conditions were not in existence at the time these beds mi^ht 

 have been laid down. The researches of Lesquereux, a digest of which is 

 given by Woodworth in Part II, make it eminently probable that the 

 Carboniferous series of this field does not begin with the lower poi-tion of 

 the Coal Measures, but with the upper part of that section. Not only are 

 the lower limestones and the Millstone grit lacking, but about half of the 

 measures which normally contain a better coal in the district west of 

 the central Appalachian axis are also lacking:. 



It should be observed that the fossils which afforded the basis for 



