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



the rninettes display evidences of much more shearing 1 than is 

 seen in the pegmatites and quartz veins. The number of the 

 minette dikes is so small, and their importance in the present 

 discussion is so slight, that they will not be considered further 

 here. 



SuiJMAKT AND CONCLUSIONS. 



(1). The JSTarragansett Basin is a body of Carboniferous 

 strata which (a) have been deformed according to the Appa- 

 lachian type of folding ; (o) have been regionally metamor- 

 phosed ; and (c) have been intruded by igneous rocks. 



(2). The Basin is surrounded on nearly all sides by a nearly 

 continuous border of pre-Carboniferous rocks from which the 

 Carboniferous sediments were derived. The border is inter- 

 rupted by the post-Carboniferous intrusives, in South Kings- 

 town, and by arms of the sea, between Narragansett Pier and 

 Sakonnet Point. 



(3). The Carboniferous strata represent sediments which 

 (a) were heterogeneous in composition, containing varying 

 amounts of feldspar, ilmenite, magnetite, carbonaceous matter, 

 etc.; (h) were deposited by fresh water; and (c) were brought 

 together and laid down by currents which had rather rapid 

 variations in direction, rate, and carrying power. 



(4). The folding of the strata in the southern half of the 

 Basin was caused by forces which acted radially, but with 

 much greater intensity along approximately east-west lines than 

 along north-south lines. 



(5). In different parts of the southern half of the Basin, the 

 deformation effected by these forces shows variations in inten- 

 sity — variations which owe their origin {a) to variations in the 

 forces ; (b) to vertical position in a given fold ; or (c) to rock 

 texture. 



(6). The intensity of the deformation, that is, the degree of 

 compression, as seen in the principal folds and in the minor 

 folding and contortion, increased southward. 



(7). The regional metamorphism is both dynamic and static. 



(8). The effects of the dynamic regional metamorphism (a) 

 are seen in all parts of the southern half of the Basin ; (b) are 

 not directly related to textural differences and to stratigraphic 

 depth ; (c) increase in intensity southward and westward. 



(9). The schistosity of the Carboniferous sediments is often 

 related, in respect to attitude, to the bedding. 



(10). The effects of the static regional metamorphism are 

 superposed upon the effects of the dynamic metamorphism and 

 are a consequence of the continuation of anamorphic chemical 

 changes after mechanical movement had ceased. 



