236 HOLLAND: CHARNOCKITE SERIES. 



and are almost certainly altered inclusions of some foreign rock. 

 The most abundant constituent of these inclusions is a microper- 

 thitic or cryptoperthitic felspar with which is associated a series of 

 typical " contact " minerals — corundum, sillimanite, rutile and green 

 spinel (pleonaste or hercynite). At the periphery of each of 

 these inclusions there is generally a concentration of biotite, flakes 

 of which exist in smaller quantities also in the charnockite around. 

 The corundum forms larger crystals than any of the other con- 

 stituents of these xenoliths ; they have an elongated barrel-shape, 

 about three times as long as they are broad, and vary in size from 

 crystals 6 or 7 inches long down to microscopic granules. Each 

 large corundum crystal is surrounded by a distinct crystallization 

 11 court" of granular felspar, slightly coarser in grain than the rest 

 of the matrix, and practically free of the other accessory minerals. 

 The felspars of the xenoliths are perfectly granulitic in structure, the 

 granules being crossed by streams of sillimanite needles, which, as 

 usual, disregard the crystal. boundaries of their host and strike 

 across the boundary lines from one granule to another. The char- 

 nockites in which these inclusions occur are well foliated, and the 

 long axes of the ellipsoids are arranged approximately parallel to the 

 foliation. The concentration of biotite around the periphery of 

 each corundiferous xenolith is probably the result of reaction 

 between the charnockite and the foreign rock. 



I can recall no cases exactly parallel to these remarkable 

 corundiferous xenoliths. Corundum, sillimanite, green spinel and 

 rutile have frequently been found in foreign fragments enclosed in 

 volcanic rocks, and in most cases they are regarded with good reason 

 as the results of contact-metamorphisnw 1 But it is of course in- 

 admissible to compare the metamorphism of inclusions in a vol- 

 canic rock with the effects produced on fragments caught up in plu- 



1 See Lacroix : " Les enclaves des roches volcaniques," 1893 ; and Lagorio : " Pyrogene 

 Korund, dessen Verbreitung und Herkunft." Zeitsc r. fur t Kryst,Vo\. XXIV (1895), pp. 

 285—299. 



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