454 Louglilin — Intrusive Granites and Associated 



are excellent exposures of granite apophyses following and 

 cutting across the foliation of the schist. The apophyses are 

 medium-grained to pegmatitic, slightly to highly muscovitic, 

 and of red to white color. The white color is more pronounced 

 in the more highly muscovitic rock. The pegmatitic and 

 muscovitic characters are best developed in the large dikes 

 ( fig. 2 ), which cut approximately at right angles to the 

 foliation of the schists. These dikes, or large apophyses, are 

 exposed at intervals along Tower Hill towards Bridgetown. 



Excavations in a graphitic bed of the schist, between one 

 and two miles south of Bridgetown, have exposed pegmatite 

 dikes and associated cjuartz veins. The graphitic rock is also 

 cut by small, branching, fibrous veins composed chiefly of 

 sillimanite, quartz, and muscovite. These veins are believed 

 to be genetically associated with the pegmatite, but no careful 

 study has yet been given them in connection with the problem 

 under discussion. 



Similar, and even more convincing, evidence is found along 

 the shore of the Bay from Little Neck northward to Hazzard's 

 quarry. The muscovitic granite with schist inclusions is the 

 prevailing rock on Little and Boston Necks. It is increasingly 

 muscovitic and pegmatitic as the contact with the schists is 

 approached. At Watson's Pier schist, cut by many large 

 dikes of the granite and pegmatite, is the prevailing rock. 

 Large pegmatite dikes are numerous along the coast as far 

 as the north end of the Bonnet, and outcrop at intervals as far 

 north as Saunderstown. From this point northward, pegma- 

 tite dikes are scarce, and the northernmost exposure seen is at 

 Hazard's quarry. Here is a small dike consisting chiefly of 

 quartz with a little feldspar and practically no mica. A few 

 quartz veins with rare feldspar crystals, exposed near the 

 summit of Barber's Heights, are the northernmost pegmatitic 

 exposures found. The evidence in the Kingstown area, there- 

 fore, appears conclusive that the granites bordering the meta- 

 morphosed Narragansett Basin sediments are members of the 

 Sterling batholith and are intrusive into the schists. Petro- 

 graphic study proves that the pegmatite dikes on Tower Hill 

 and along the shore of the Bay are not independent intrusions, 

 but apophyses from Sterling batholith, tending to grade into 

 quartz veins as the distance from the batholith increases. 

 Evidence in the whole area studied has proved that the gran- 

 ites of southwest Rhode Island, south of the Washington Co.- 

 Kent Co. boundary (fig. 1) are not of pre-Cambrian age as 

 previously supposed, but belong to the Sterling batholith, the 

 youngest formation (including the Westerly granite dikes) of 

 the area. 



Time of Intrusion. — The details of metamorphism in the 



