in the Narragansett Basin. 61 



upper conglomerate a few pebbles resembling the gneissoid 

 Sterling type were found. None resembling the muscovitic 

 contact phase of the Sterling type were noted. Occasional small 

 arkose pebbles identical in composition with typical beds in the 

 " Coal Measures" were also found, but only in a few outcrops. 

 This evidence indicates that the red (Wamsutta) strata and the 

 overlying conglomerate were derived from one general source 

 and in one continuous period of deposition, the earlier part of 

 which was marked by an abundance, and the latter part by a 

 scarcity, of the line red matrix. The presence of " Coal 

 Measures " arkose and Sterling granite pebbles in the coarse 

 conglomerates favors its correlation with the Dighton conglom- 

 erate, which is regarded by the writers as of Permian age. 



The part of the Norfolk Basin east of Canton Junction has 

 been described* as consisting essentially of the north limb of 

 a syncline, bounded by a profound fault on the south side 

 and by an unconformable contact along the Quincy granite of 

 the Blue Hills on the north side. This eastern part of the 

 Basin thus lies in an opposite attitude to the western part. 

 The strata present are a local basal conglomerate of extreme 

 coarseness overlain by the series of red beds. The upper 

 conglomerate is not represented. The basal conglomerate 

 contains pebbles of both Quincy and Dedham granite, and 

 the red strata pebbles of the Dedham granite. An occasional 

 small arkose pebble of the " Coal Measures " type was also 

 found. The presence of these occasional arkose pebbles in the 

 red strata further suggests their correlation with the Permian, 

 and this tentative correlation is indicated in the table on page 

 63 ; but owing to the scarcity of the arkose pebbles and to the 

 absence" of fossils of critical value, the writers refrain from 

 committing themselves to more than a tentative correlation. 



It is interesting in this connection to note the presence west 

 of the Blue Hillsf (fig. 1) of an isolated outcrop of altered 

 sandstone with black carbonaceous partings, of the same general 

 character as beds in the " Coal Measures " (fig. 1). Its complete 

 isolation prevents more than this mere suggestion of correlation 

 based on lithologic appearance. 



The Boston Basin. 



The Boston Basin strata consists chiefly of the Eoxbury 

 conglomerate and the overlying Cambridge slate. The con- 

 glomerate has generally been regarded as equivalent to the 



*W. O. Crosby has given a detailed description of this area ; (Geology of 

 the Boston Basin, vol. 1, Part 3, The Blue Hills Complex. Boston Soc. Nat. 

 Hist.). 



A summarized description has been given by G. F. Loughlin ; this Journal 

 (4), vol. xxxii, pp. 17-32, 1911. 



•f See also this Journal (4), xxxii, p. 26, fig. 2. 



