F. H. Lahee — Metamorphism and Geological Structure. 251 



ridges of harder rocks. A few inliers of the harder rocks 

 occur surrounded by the Carboniferous (see Hg. 1). On all 

 sides, except in the broken southern rim, the same statements 

 hold true, namely, that the predominating border rocks are 

 granites or granite gneisses and that these granites are intrusive 

 into sedimentary formations, now much metamorphosed. The 

 granites (Sterling granite series) in South Kingstown are prob- 

 ably post-Carboniferous and the schists enclosed in them, 

 Carboniferous ;* but, elsewhere the phitonics are pre-Carbon- 

 iferous, as is proved by the presence of their disintegrated 

 debris in the Carboniferous. 



The strata of the Basin are shales, sandstones, arkoses, and 

 conglomerates, which have been folded, metamorphosed, and 

 injected by an acid series of dikes and veins, offshoots from the 

 post-Carboniferous granites of Kingstown. The anticlines are 

 relatively long and narrow, after the Appalachian pattern, and 

 crumpling of minor dimensions often occurs superposed upon 

 the major folds. Although there are innumerable exceptions, 

 the metamorphism, regarded from a broad standpoint, is dis- 

 tinctly greater in the southern part of the field than in the 

 northern. The acid intrusives range in composition from highly 

 feldspathic pegmatites to veins of pure massive quartz. More- 

 over, they are much larger, and there are many more of them, 

 in South Kingstown than farther northward and eastward. 



Throughout the Basin, then, the texture and composition of 

 the sedimentary rocks, the complexity of the folding, the 

 degree of metamorphism, and the composition and abundance 

 of the acid dikes, are variable factors. It has been our aim to 

 investigate the kinds and degrees of metamorphism and to 

 correlate them with the other variable factors just mentioned, 

 with stratigraphic depth, and with geographic position in the 

 Basin. The greater portion of the work has been carried on 

 in the southern half of the field, where the exposures are more 

 satisfactory. 



The first part of this paper will treat of the Structural Geol- 

 ogy of the Carboniferous rocks ; the second, of the Petrology 

 and Metamorphism of the Carboniferous rocks; and the third, 

 of the post-Carboniferous intrusives. There is no need of 

 describing the pre-Carboniferous rocks in detail. Their impor- 

 tance for us rests (1) upon their having constituted the floor 

 upon which the Basin sediments were laid down, and (2) upon 

 their relations to the forces which deformed these sediments ; 

 and these matters will be taken up under the other heads. 



The remark is perhaps unnecessary that no attempt could be 

 made to obtain exact quantitative results, because the relations 



*Loughlin, G. F., Intrusive Granites and Associated Metamorphic Sedi- 

 ments in Southwestern Rhode Island, this Journal, xxix, p. 447, 1910. 



