280 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the finer grained xenolitlis the grain is quite uniform and will average 

 under a millimeter; in the coarser, the grain may average from one to 

 three millimeters or about the same as that of the fine-granite so 

 abundantly developed in the eastern part of the area. The general 

 texture of this type is granitic, with a feeble and usually irregular 

 porphyritic tendency. The phenocrysts of feldspar, sometimes with 

 quartz, may be clustered in patches of coarser granitic habit. Some 

 trace of an inner core of distinct form may be seen in at least some of 

 the feldspar phenocrysts, even in the coarsest grained types, but the 

 phenomenon is more distinct in the finer grained ones. The feldspar 

 in many of the xenoliths is precisely similar to that of the granite 

 outside, except in size. In others there is a more distinct separation 

 of the microcline and albite. Sometimes separate crystals of almost 

 pure microcline and albite may be seen; but generally the two are 

 intergrown, the microcline forming relatively good sized patches 

 surrounded by finely twinned albite which determines the outlines of 

 the crystal. The quartz is highly xenomorphic in some, in others it is 

 rounded in outline and may be inclosed in the feldspar. 



The pyroxene is aegirite. It is in part massive, of the same charac- 

 ter as that of the granite, and is to some extent intergrown with rie- 

 beckite. The larger massive grains lie about the feldspar, sometimes 

 enclosing them. Much of the aegirite is found lying l>etween the 

 feldspar crystals and penetrates quite deeply into their margins. In 

 such instances it is of very irregular habit often being little more than 

 a skeleton of loosely joined grains and minute prismoids tending to 

 form a single elongated crystal. Sections cut through these irregular 

 aegirites where they penetrate into the feldspar gWe the impression of 

 a "spatter" of aegirite grains enclosed in the middle of a feldspar 

 crystal. Aegirite in the form of small microlites together with shreds 

 and fibers of blue hornblende are scattered through the feldspar gen- 

 erally. In some of the xenoliths, fluorite is not only present in the 

 form of minute grains in the aegirite (as in the granite) but it also 

 forms masses of considerable extent replacing the quartz. Occurring 

 with it and of the same habit, is zircon. These minerals are both 

 prolmbly of pneumatolytic origin. Titanite is also present in formless 

 grains and is perhaps of similar origin with the zircon. 



Other inclusions in the Granite-Porphi/ry. The rarity of cognate 

 xenoliths in the granite-porphyry of the Rattlesnake Hill type has 

 been noted; also the occurrence in some parts of the porphyry, of 

 very fine grained, angular fragments. These are perhaps best exposed 

 for study in the vicinity of Scamaug Notch, and in many of the 



