ORIGIN OF THE PEGMATITES OF MAINE 317 



throughout the magma which gave rise to these pegmatites, over the 

 percentages in bordering pegmatite magmas, or else to differing 

 degrees of magmatic segregation in magmas whose average composi- 

 tion was similar. As already explained, quartz associated with lepido- 

 lite and clevelandite from the gem-bearing portion of one of these 

 pegmatites showed low-temperature characters, and the unusual 

 abundance of pockets indicates that these portions were richer than 

 the normal in gaseous constituents, probably mainly water vapor. 

 In general therefore the gem-bearing pegmatites were characterized 

 by a higher percentage of sodium,, lithium, and phosphorus than the 

 normal pegmatites, and probably by more water vapor and a slightly 

 lower temperature of crystallization. 



The region characterized by pegmatites rich in fluorine minerals 

 but not in the lithium minerals forms an area only a few miles across 

 in the town of Stoneham and bordering parts of other towns in Oxford 

 County and the town of Chatham, New Hampshire. 



Bearing of broad geologic relations on genesis. — The broad geo- 

 graphic relationships of the granites and pegmatites are also significant 

 of their relationship and origin.' Many of the granite areais of the 

 eastern portion of Maine are characterized by sharp boundaries, 

 while most of the granite areas of southwestern Maine show very 

 indefinite boundaries and are bordered by large areas of slates and 

 schists which have been intruded by various amounts of granite- 

 gneiss and pegmatite and by some granite and diorite. The contrast 

 between the two types of contacts is well shown within the areas of 

 the Penobscot Bay' and Rockland^ folios. In many parts of the 

 latter area, notably along the granite-schist contact from Bluehill 

 village northward and from Bluehill Falls southwestward to Sedgwick, 

 the granite preserves its normal medium grain up to the exact contact. 

 In most places this contact is so sharp that it is possible to stand with 

 one foot resting upon typical Ellsworth schist and the other foot 

 resting on normal granite. Dikes and irregular intrusions of granite 

 are not very abundant in the schists near the main granite masses, 

 and flow-gneiss, pegmatite, and basic differentiations from the granite 

 magma are almost entirely absent. In the Rockland quadrangle, 



1 Geologic Atlas U.S., folio No. 149, U.S. Geol. Survey. 



2 Ibid., folio No. 158. 



