and the Adjacent Sedimentary Formations. 31 



ous, are younger than all the granites which lie adjacent to 

 them, including a reddish biotite granite. Fossil plants,* 

 found at certain points in both the Narragansett and the 

 adjoining contiguous Norfolk Basin, are the principal evi- 

 dence of the Carboniferous age. The questions now arise : — 

 (1) are there in the region two batholiths of reddish biotite 

 granite, one non-gneissoid, but epidotized, and older than 

 all the sediments, and the other gneissoicl, but not greatly 

 epidotized, and younger than all the sediments? (2) Do 

 both granites belong to the same batholith, in portions 

 of which the gneissoid structure was developed by com- 

 pressive forces acting during, or closely after, intiaision, 

 and in other (or in part the same) portions of which epidotiza- 

 tion was developed by much later compressive forces acting 

 long after the granite had become rigid and had cooled far 

 below its crystallization temperature. If the latter case can 

 be proved, there must be a pronounced unconformity separat- 

 ing these sediments of the Narragansett Basin older than the 

 granite from those in the Narragansett and Norfolk Basins 

 which are younger than the granite, f 



The above questions, suggested by the facts presented in this 

 paper, outline further interesting problems to be investigated 

 in the region of eastern Massachusetts and Rhode Island ; but 

 their solutions may depend upon the study and solution of 

 many minor problems throughout the whole region. Some of 

 these more special problems are now under consideration. 



Summary. 



The igneous rocks in the ai*ea studied include an altered bio- 

 tite granite series, an older felsite series, the Quincy alkaline 

 granite series, and alkaline felsite ; the sediments, much folded, 

 are the conglomerates, sandstones and slates of the Boston and 

 Norfolk Basins. The principal boundaries between sedimentary 

 and igneous rocks are faults of nearly east-west trend, with one 

 exception — along the south edge of the Quincy granite mass, 

 where the basal and strictly local " giant conglomerate" is com- 

 posed chiefly of bowlders of Quincy granite-porphyry. At no 

 other place have pebbles of the Quincy granite series been 

 found in the sediments of either basin. The evidence leads to 

 the conclusion that the Quincy granite mass formed a low 

 prominence which suffered erosion for a time, but was soon 



* Crosby and Barton, this Journal, vol. xx, ser. 3, 1880, pp. 416-420; 

 Shaler, Woodworth, and Foerste, U. S. Geol. Surv., Mon. xxxiii, 1899. 



t J. B. Woodworth (Mon. xxxiii, U. S. Geol. Surv., 1899, p. 186) sug- 

 gested that an unconformity might exist in the upper portion of the Naria- 

 gansett sediments, and that the younger of the sediments might then be 

 correlated as Permian. 



