3IO EDSON S. BASTIN 



is much less common in the case of the pegmatites, but was never- 

 theless observed at several localities. On the highest portion of 

 Streaked Mountain a number of patches of schist a few square yards 

 in area were seen apparently entirely inclosed by pegmatite. Small 

 schist fragments are also inclosed by pegmatite in the Boothbay Har- 

 bor region. Dr. W. H. Emmons of the U.S. Geological Survey, 

 who visited Mt. Mica a year later than the writer, when the excavation 

 had proceeded farther, observed schist fragments in the pegmatite 

 there a few feet below the schist hanging wall. These appeared to 

 have been wholly inclosed by pegmatite, and the schistosity of the 

 fragments made large angles with the schistosity of the walls from 

 which they were evidently dislodged. The pegmatite shows no 

 bending of the minerals or other changes in character near the frag- 

 ments. In the instances cited the schist fragments appear to have 

 been caught up while the pegmatite mass was still partly or wholly 

 fluid, and the specific gravity of ^"e magma was sufficient, at least in 

 the Mt. Mica example, to float the fragments. 



Temperatures of pegmatite crystallization. — Some evidence in 

 regard to the temperatures of the pegmatites at the time they crystal- 

 lized has been obtained from studies of quartz by Wright and Larsen,' 

 a number of the specimens being collected by the writer from the 

 pegmatites of Maine and other parts of New England. 



Studies of these writers and of earlier observers have shown that 

 at about 575° C, quartz undergoes a sudden change from one form 

 of crystal symmetry to another. Wright and Larsen have defined 

 the criteria which may be applied to distinguish the quartz which 

 crystallized below 575° and that which crystallized above that tem- 

 perature and has undergone reversal in the solid state upon cooling. 



No granites of Maine were tested by these experimenters, but 

 thirteen specimens of granite gneisses and quartz porphyries from 

 other regions show as a rule the characters of high-temperature 

 quartz, thus placing their final crystallization above 575° C. 



Quartz from a dike of fine-grained pegmatite from one to four 

 feet wide, which intrudes biotite granite near Rumford Falls, is of 

 the high-temperature variety. This dike is typical of many of the 



I F. E. Wright and E. S. Larsen, "Quartz as a Geologic Thermometer," Anier. 

 Jour. Sci., XXVIII (June, 1909), 423-47. 



