440 WARREN AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



Igneous rocks. 

 Pre-Cainbrian. 



Gabbro. 



Cuinberlandite. 



Labradorite porphyry dikes. 

 Middle Devonian. 



Quartz diorite. 



Milford granite. 



Grants Mills granite, including fine granite. 



Joes Rock granite, including quartz porphyry, feldspar i)()rphyry. fine 

 granite, and felsite. 

 Lower Pennsylvanian. 



Diamond Hill felsite. 

 Middle Pennsylvanian. 



Riebeckite-segirite granite. 



Riebeckite granite porphyry. 



Diamond Hill quartz veins. 

 Sheldonville quartz vein. 

 Post-Permian. 



Diabase dikes. 



Pre-Cambrian Rocks: Blackstone Series 

 nomenclature 



In the region southeast of Woonsocket and west of Providence there 

 occur two large areas and several small areas of highly metamorphosed 

 rocks referred by Woodworth^ to the pre-Cambrian and named the Black- 

 stone series. They consist of green schists, quartzites, and some lime- 

 stones. These metamorphic rocks occur as huge isolated blocks in granite. 

 On one side only they are in contact with the Carboniferous sediments, 

 and this contact is either a fault or an unconformity. 



The largest of the "blocks" extends from Lonsdale, northwest of Paw 

 tucket, to Copper Mine Hill. The northern half of it is shown in tlui 

 accompanying map. The other occurrences of the Blackstone series are 

 south of the area here mapped. 



Woodworth divided the rocks of the series into three formations — the 

 Cumberland quartzites, the Ashton schists, and Smithfield limestones. 

 He did not map these formations, but used the names as locality terms. 



Emerson and Perry^ separated the series into four formations, dividing 

 the schists into two parts. They named the quartzite from a similar 

 rock at Westboro, Massachusetts. These subdivisions, with their relative 

 positions, are as follows: 



'Monograph TT. S. Geol. Survey No. 33. p. 104. 

 8 Bull. U. S. Geo]. Survey No. 311, p. 10. 



