ORIGIN OF THE PEGMATITES OF MAINE 309 



where softening is shown, being sharp, and the pegmatite next the 

 contact showing no difference in composition from that at some dis- 

 tance away. Where schist fragments are inclosed in the pegmatite 

 their sharp outlines are preserved. 



If the physical conditions of the pegmatite and granite magmas 

 were notably different at the time of their intrusion, it would be 

 natural to expect some differences in the forms assumed by the granite 

 and pegmatite masses. While in many cases the forms assumed 

 by the two types of rocks are similar there is in general a tendency for 

 the smaller pegmatite intrusions in the foliated rocks to assume the 

 form of a succession of lenses while granite intrusions of similar size 

 tend to be more nearly parallel-walled. This contrast is particularly 

 noticeable in the Boothbay Harbor region and near Rumford Falls 

 and is probably expressive of slightly greater rigidity in the granite 

 than in the pegmatite magma and also of greater softening of the 

 inclosing schist by the pegmatite than by the granite magmas. The 

 great size of certain pegmatite masses, such as Streaked Mountain 

 in Hebron, is on the other hand suggestive of physical conditions in 

 some pegmatite magmas not widely different from those obtaining 

 in normal granite magmas. The crest of Streaked Mountain was 

 examined for over half a mile of its length, and the width of outcrop 

 examined across the trend of the ridge was also about half a mile. 

 The whole area traversed and the remainder of the mountain as far 

 as it could be seen was underlain almost exclusively by coarse peg- 

 matite, the mountain being a "boss" of this material. The pegmatite 

 is of the usual granitic type and exhibits no more than the usual amount 

 of variation in texture and composition from point to point. It is 

 difficult to conceive of a mass of this size and general uniformity 

 crystallizing under anything like vein conditions. With very high 

 gaseous content and correspondingly high mobility it would be natural 

 to expect more differentiation both in texture and composition. It 

 seems probable that the specific gravity and the viscosity of such a 

 pegmatite magma was not so much below that of a granite 

 mass intruded under similar conditions as has been commonly 

 supposed. 



Fragments of the wall-rock are very frequently inclosed by the 

 border portions of the granite masses of Maine. The phenomenon 



