354: F. H. Lahee — Metamorphism and Geological Structure. 



Art. XXXIII. — Relations of the Degree of Metamorphism 

 to Geological Structure and to Acid Igneous Intrusio7i in 

 the Narragansett Basin, Rhode Island ; by F. H. Lahee. 



(Continued from p. 262.) 



Part II. 



Contents. 



Petrology of the Carboniferous sediments. 

 Introductory remarks. 

 Study of the specimens. 

 Coals. 

 Pelites. 

 Psammites. 

 Psephites. 

 Summary. 

 Relations of the degree of metamorphism to rock-texture. 

 Geographical distribution of the degrees of metamorphism. 

 Relations between the degree of metamorphism and stratigraphic depth. 

 Relations between the degree of metamorphism and the intensity of 

 the folding. 

 Strikes. 

 Dips. 

 Pitch. 



Axial planes. 



Relative number of folds across the Basin. 

 Minor folding. 

 Relations of the schistosity to the bedding. 

 Conclusions, 



Petrology of the Carboniferous Sediments. 



Introductory Remarks. — Aside from the effects of meta- 

 morphism, the Carboniferous formation of the Narragansett 

 Basin consists of a series of shaly, sandy, and conglomeratic 

 rocks, which are notable (1) for their rapid textural variations, 

 both parallel and perpendicular to the bedding ; (2) for the 

 abundant presence in them of such lithologic structures as local 

 unconformity and cross-bedding ; (3) for the considerable 

 j:>roportion of soluble clastic minerals in them ; and, (4) for 

 their content of fossil land organisms and coaly layers, with a 

 total absence of anything marine. Although these features 

 may be said to characterize the formation as a whole, they do 

 not all belong to all horizons. The evidences point (1) to a 

 prolific source of materials ; (2) to the incompleteness of 

 chemical weathering here in Carboniferous times ; and, (3) to 

 rapid deposition by stream action, partly on land and partly in 

 standing bodies of fresh water. 



After the Carboniferous strata were laid down, they were 

 folded and metamorphosed, the original minerals being recrys- 

 tallized in some cases or breaking up and recombining to form 



