52 Loughlin and Hechinger — Unconformity 



Measures" as resting unconformably on Cambrian quartzite 

 and granite, and as containing large pebbles of the granite. 

 These structural features are, in the main, confirmed b} 7 Emer- 

 son and Perry,* who describe the Carboniferous conglomerate 

 resting on the Milford granite, but their microscopic study 

 of the granite pebbles proves them all to belong to the East 

 Greenwich type and none to the Milford. At one place 

 near Natick they describe " a contact of the Milford granite 

 and the conglomerate which might be interpreted as an intrusive 

 contact, since it . . . cuts across the laminae of the sericite schist 

 (metamorphosed Carboniferous). The alteration of the rock 

 here is probably due to crushing. The extreme metamorphism 

 of the conglomerate, combined with the small amount of mash- 

 ing and jointing, is very characteristic." Farther north, in 

 Cranston, R. I., they describe a few places where the Carbonif- 

 erous conglomerate and Milford granite become intimately 

 blended along the contact. These descriptions, both of struc- 

 tural relations and of total absence of Milford granite 

 pebbles in the conglomerate, convey to one who has only 

 studied the contact along the undoubtedly intrusive Sterling 

 granite gneiss the impression that the Milford granite also 

 is intrusive into the "Coal Measures" conglomerate; Emerson 

 and Perry, however, regard the conglomerate as resting uncon- 

 formably on the granite. There is, nevertheless, no question 

 that there is a total absence in the "Coal Measures" con- 

 glomerate of any pebbles of the Sterling, Northbridge, Mil- 

 ford, and Dedham types of gneiss and granite. The writers 

 were able to study outcrops remote from the contact only in 

 the area between Providence and the northern boundary of 

 the Basin, and here also no trace of any of the granites in ques- 

 tion was found. Pebbles of a quartz-felsite porphyry with 

 white weathered surfaces are numerous in the conglomerate 

 exposures of this area, but their microscopic characters are so 

 obscured by alteration that the writers can not determine their 

 source. 



Fossil plants and insects have been found in the " Coal 

 Measures" at a number of localities,! and have been deter- 

 mined by Lesquereux as equivalent to the Upper Carboniferous 

 or Pennsylvanian. One species, Sigillaria volzii, found west 

 of Plainville, Mass., is stated by him to be rare in the "Coal 

 Measures" of America, one specimen being seen by him from 

 the Plymouth F vein in Pennsylvania, a horizon near the top 

 of the anthracite field.;}: Haynes,§ in 1912, found impressions 



*U. S. Geol. Survey, Bull. 311, pp. 39-40, 1907. 



f Lists of these fossils are given by Woodworth, op. cit., pp. 202-205, 

 after Lesquereux and Scudder. 



X Cited by Woodworth, op. cit., p. 181. 



§ Hayues, W. P.. Discovery of bivalve Crustacea in the Coal Measures near 

 Pawtucket, R. I., Science, newser., vol. xxxvii, pp. 191-192, 1913. 



