IGNEOUS ROCKS 467 



granite with its abundant aegirite, which appears to be the case. A sim- 

 ilar variation has been noted in the Quincy granite as compared with its 

 fine granite and porphyry phases.^^ The Sokotra gi'anite, thougli higher 

 in silica and somewhat lower in total iron, is still strikingly similar in 

 general character. The very low lime and magnesia are striking charac- 

 teristics of all three. 



A few quartz veins, up to a foot in width, are found in the granite and 

 these often carry considerable fluorite. One small vein (one inch) of 

 riebeckite has been noted. 



Crocidolite from Beacon Pole Hill, occurring in masses up to an inch 

 or more in diameter, associated with dolomite, quartz, and fluorite, has 

 been described by A. H. Chester and F. T. Cairns,^^ who give an analysis. 

 According to this, it corresponds quite closely to the riebeckite of the 

 Quincy pegmatites. ^^ 



As variations from the normal type above described we may note the 

 occurrence, on the northwest side of the main mass, of a more coarsely 

 crystalline variety in which crystals of riebeckite measuring up to 2 centi- 

 meters in length and 0.7 millimeter in breadth and large quartz crystals 

 are present. This coarser phase appears in places to occur in the normal 

 granite in the form of irregular patches. 



Two miles south of Iron Mine Hill, on the road to Cumberland village, 

 an intensely sheared phase of the granite occurs. Thin-sections show 

 onty riebeckite with the crushed microperthite and quartz. 



Inclusions. — In one of the quarries several inclusions were found, oiio 

 of which is unmistakably a fragment of the near-by biotite granite. An- 

 other has been so largely recrystallized that its original character is rather 

 doubtful. The granite inclusion, though somewhat modified, possesses 

 the mineral and textural features belonging to the biotite granite, but 

 now contains considerable fluorite derived from the inclosing granite. 

 The other inclusion is now largely a mass of biotite flakes, recrystallized 

 feldspar, quartz, and fluorite. The flnding of the granite inclusion is of 

 great importance, for it shows conclusively that the alkaline granite is 

 intrusive into the biotite type. This relation is also borne out, as will be 

 noted later, by similar inclusion in the riebeckite porphyry dike near 

 Sneech Pond and by the actual chilled contacts of the riebeckite por- 

 phyry against the Milford granite. 



Rich eclcite-h earing granite porphyry. — A riebeckite-bearing granite 

 porphyry outcrops in several localities : in the Cumberland dike west of 



37LOC. cit, p. 295. 



38 Am. Jour. Sci.. vol. 34, 1887, p. 108. 



^ Proc. Am. Acad. Arts and Sci., vol. xlvli, No. 4, July, 1911, p. 154. 

 XXXIII— Bull. Gbol. See. Am., Vol. 25, 1913 



