THE 



JOURNAL OF GEOLOGY 



MAY-JUNE, igio 



ORIGIN OF THE PEGMATITES OF MAINE' 



EDSON S. BASTIN 

 U.S. Geological Survey 



During a portion of the summers of 1906 and 1907 I had the 

 opportunity to study in some detail the pegmatite deposits of Maine, 

 and at intervals during succeeding years have been able to pay brief 

 visits to commercially important pegmatite deposits in Connecticut, 

 New York, Pennsylvania, and Maryland. Without entering into the 

 details of the field occurrences, which will be described in a forth- 

 coming bulletin of the U.S. Geological Survey, I wish to summarize 

 here the more important scientific results of these studies. Particu- 

 lar acknowledgment is due to Dr. Whitman Cross of the U.S. Geo- 

 logical Survey, for valuable criticism and advice in this work. 



The pegmatite -deposits in the state of Maine all belong to the type 

 commonly known as granite pegmatite, its dominant minerals being 

 the same as those which are most abundant in ordinary granites. 

 Pegmatites are most abundantly developed in the western and south- 

 western part of the state, and are invariably associated with granites. 

 Excellent exposures in the feldspar and gem quarries, on glaciated 

 ledges, and especially along the seashore in the Boothbay Harbor 

 region, afford unusual opportunities for detailed field studies. 



General geologic relations.- — The pegmatite masses vary in size 

 from extremely small stringers intimately injected between the foliae 

 of schists and thus forming injection gneisses, to batholitic masses 



I Published with the permission of the Director of the U.S. Geological Survey. 

 Vol. XVIII, No. 4 297 



