366 F. H. Lalxee — Metamorphism and Geological Structure. 



Geographical Distribution of the Degrees of Meta- 



morphism. 



Some investigators in this region have noticed differences in 

 the intensity of metamorphism in passing across belts two or 

 three miles in breadth. Dale observed that the Carboniferous 

 strata have been more metamorphosed on Conanicut and Dutch 

 islands than in southern Aquidneck Island.* Foerste showed 

 that the rocks of Prudence Island are less altered than those 

 of Hope Island.f And both FoersteJ and Collie§ remarked 

 upon the increase in metamorphism westward across northern 

 Conanicut Island. In our field studies we have found a 

 like advance in metamorphism eastward and westward from 

 the middle north-south strip of the western coast belt 

 north of East Greenwich ; southward, in the western coast 

 belt, south of Wickford ; and eastward, from Aquidneck 

 Island to the eastern coast belt. These variations are not uni- 

 form and, in some cases, are not very conspicuous. 



Of more importance is a study of the distribution of the 

 degrees of metamorphism in the Basin as a whole. This we 

 have done graphically as follows : The position of the eight 

 hundred or nine hundred specimens examined was plotted on 

 the map. For each of these, the kind of rock (coal, shale, 

 sandstone, or conglomerate) was indicated by a symbol, and 

 the stages of metamorphism (A, B, C, and D) were shown by 

 four different colors. The map was then divided into four 

 equal rectangles, as in fig. 21, and the allotment of the speci- 

 mens determined. The results are tabulated below. 



Conglomerate Sandstone Shale Coal Totals 

 NE. rectangle : 



Stage A : 3 3 



Stage B : 2 8 4 14 



Stage C : 2 2 4 



Stage D : 



Totals : 



2 



10 



9 







21 



. rectangle : 













Stage A : 



2 



5 



1 



1 



9 



Stage B : 



1 



2 



1 







4 



Stage C : 



4 



6 



2 



1 



13 



Stage D : 







1 



1 







2 



Totals : 7 14 5 2 28 



*Dale, T. N., The Geology of the Mouth of Narragansett Bay. Proe. 

 Newport Nat. His. Soc, Doc. 3, 1884, p. 6. 



fShaler, N. S., Woodworth, J. B., and Foerste, A. F. : Geology of the 

 Narragansett Basin. U. S. G. S., Monog. xxxiii, 1899. p, 241. 



% Ibid., p. 230. 



$ Collie, G. L., Geology of Conanicut Island, R. I. Trans. Wise. Acad., x, 

 1894-1895, pp. 201, 217. 



