448 Loughlin — Intrusive Granites and Associated 



B. K. Emerson and J. H. Perry* in 1907 described and 

 mapped the formations along the western border of the E"arra- 

 gansett Basin. The southern end of their area overlaps the 

 northeast corner of the area here discussed, but no contacts are 

 there exposed. They also mapped the granite as pre-Cambrian 

 (fig. 1 of this paper). 



Resume of Evidence in S. M Connecticut. 



As the writer's work here described has been essentially a 

 continuation of his studies in southeastern Connecticut, a sum- 

 marized statement of the character and relations of the granite 

 and adjacent metamorphic sediments in that area is here given 

 to serve as a basis for correlation, f A portion, also, of the 

 map is copied (fig. 1, west of long. 71° 45' and north of lat. 

 41° 25'). 



The metamorphic sedimentaries shown in the map are a 

 quartzite ( Plainfield quartz-schist ) and a more extensive 

 quartz-biotite-schist, more or less feldspathic ( part of the Put- 

 nam gneiss series ). These, and closely related metamorphics 

 not shown in the map are characterized by the general predomi- 

 nance of plagioclase wherever feldspar is present. The com- 

 position of the plagioclase ranges from Ab 3 An x to AfyAn,. 

 They are possibly of Carboniferous age. 



The granite — Sterling granite series — mostly of pink color 

 and gneissoid structure, includes three varieties : normal biotite- 

 granite, porphyritic biotite-granite, and alaskite. . The alaskite 

 is known to cut the other two varieties, but all gradations in 

 composition and texture appear. All the varieties are intrusive 

 into the sedimentary series. Pegmatite and aplite, in sheets 

 and dikes, cut the granite series, and are abundant in the meta- 

 morphic sediments. The granite series is characterized by a 

 well-developed microline, in some cases microperthitic, white 

 oligoclase, or albite, and some quartz. 



The relation of the micro-textures of the granites to regional 

 metamorphism has been treated at some length in the original 

 paper, with the conclusion that the normal and porphyritic 

 types were intruded and crystallized while the disturbing forces 

 were most active, and that the alaskite became solid during the 

 waning stage of regional movement. This relation, if the sedi- 

 mentary series includes Carboniferous rocks, correlates the time 

 of metamorphism and intrusion with that of the Appalachian 

 Revolution. The question of age will be furthur considered 

 towards the end of this paper. 



* The Green Schists and Associated Granites and Porphyries of Ehode 

 Island, U. S. G. S, Bull. 311, 1907. 



f By permission of the Director of the U. S. Geol. Survey. 



