300 



EDSON S. BASTIN 



similar. The principal variations in composition involve (i) an 

 increase in silica, (2) an increase in sodium and lithium, and (3) an 

 increase in fluorine. The increase in silica content manifests itself in 

 a greater abundance of quartz. Pegmatites unusually rich in quartz 

 are less common in Maine than in certain other pegmatite districts of 

 the eastern United States, but it is quite possible that many of the 

 quartz dikes occurring in southern Maine were derived from pegmatite 



v» 



covered 



'-I ^ . -» V ^ ^ 

 \s f 1^^ 1/ 



^matik' >"',_; 





Fig. 2. — A quartz offshoot from pegmatite, 2^ miles northeast of Paris. The 

 branch vein is pegmatite for a short distance beyond the main pegmatite mass, but 

 beyond this grades into pure quartz. The area illustrated is about 4 feet square. 



magmas. This is suggested by the fact that certain of these masses 

 contain occasional crystals of feldspar, black tourmaline, or beryl. 

 In one instance, the transition from pegmatite to quartz vein, illus- 

 strated in Fig. 2, was observed. The second variation, involving an 

 increase of sodium and lithium, shows itself in the development of 

 occasional pegmatite masses which are rich in albite, lepidolite, spodu- 

 mene, colored tourmaline, and amblygonite. The tourmaline mines 

 of the state are in deposits of this type. The third variation, involving 

 an increase in the fluorine content, is exemplified by occasional peg- 

 matite masses which contain topaz, fluorite, herderite, hamlinite, 



