64 Loughlin and Hechinger — Narraganseit Basin. 



the weakest point in the argument, owing to the scarcity in 

 them of "Coal Measures" pebbles, and to the present 

 indefinite state of correlation of the Dedham, Milford and 

 Sterling granites, and it is hoped that others will have an 

 opportunity to gather more evidence which will afford a more 

 convincing determination of the question. So far as the 

 writers' experiences go, it seems that the answer to this 

 question may best be found through a correlation of the 

 different biotite-granite areas (save the East Greenwich). 

 There is at present in the writers' opinion no convincing 

 evidence of more than one general age for these extensive 

 granite masses ; in other words, no proof that they are not 

 parts of one immense complex batholith. If future discoveries 

 of fossils in the Pondville and Wamsutta strata shall prove them 

 to be of Pennsylvanian age, they will also prove the Dedham 

 and Milford granites to be distinctly older than the Sterling. 

 If, on the other hand, further work proves that the biotite 

 granites are all parts of one batholith, which varies from place 

 to place in textural features, or in the relative prominence of 

 micas and hornblende, the Permian age of the Pondville 

 conglomerate and Wamsutta formation will be a necessary 

 corollary to the proof. In this case the granites, both the 

 biotite and the later alkaline types, which have heretofore 

 necessarily been designated merely as post-Cambrian, may be 

 classed within the narrow limits, late Pennsylvanian and early 

 Permian. This involves a very profound period of intrusion, 

 upheaval, and erosion between these two ages which in general 

 have been regarded as closely associated ; but proof of such a 

 great time break has already been presented in this paper. 



In conclusion, the writers wish to remind their readers that 

 while the unconformity between the " Coal Measures " and the 

 Dighton conglomerate and the Permian age of the latter are 

 offered as final conclusions, the tentative assignment of the 

 Pondville conglomerate and Wamsutta formation to the Permian 

 and the correlation of the biotite granites as parts of one 

 extensive complex batholith must be regarded as working 

 hypotheses. No matter whether these hypotheses are finally 

 proved or disapproved, in either case a valuable contribution to 

 the local geology will have been made. 



The writers wish here to express their sincere thanks to 

 David White, Arthur Keith, and Laurence La Forge of the 

 U. S. Geological Survey, and to Profs. W. O. Crosby, C. H. 

 Warren, and H. W. Shimer of the Massachusetts Institute of 

 Technology, for their helpful comments and suggestions, and 

 to Miss M. G. Wilmarth of the U. S. Geological Survey 

 for invaluable clerical assistance during the preparation of 

 this paper. 



