f)i4 



major portion of the collection studied, twenty-one fresh 

 or altered dunites or pyroxenic peridotites and pyroxenites 

 contained picotite and no pleonaste or ilmenite. Six slid.-; 

 of the quartz carbonate rock, later to be described as 

 altered dunite, all contained picotite and no ilmenite. 

 Eleven rocks all containing felspar and including anortho- 

 sites, gabbros, hypersthene gabbros, olivine gabbros, and 

 gabbro very poor in felspar, all contained pleonaste (six 

 with graphic intergrowth of pleonaste and pyroxene). They 

 contained no spinel or ilmenite, with the possible excep- 

 tion of a single very small isotropic brown grain, perhaps 

 chromite in the hypersthene of one rock. Three rocks 

 (two gabbros and one hypersthene gabbro) contained 

 ilmenite and no spinel ; and nine slides of anorthosite, 

 ophitic gabbro contained no primary ilmenite or spinel. In 

 only one rock did picotite and pleonaste definitely occur 

 together. This is not plutonic but a hypersthene gabbro 

 poi ph\ tv with granophyric pleonaste. It contains a large 

 !lalhi-v crystal almost an inch in diameter, pseudiunnipi^ 

 after olivine, and in a section one large grain of picotite. 

 It seems therefore, by no means certain that the picotite 

 with the diallage in this rock are not xenocrysts derived 

 from a coarsely crystalline diallage peridotite broken or 

 partially absorbed by the intrusion of gabbro porphyry. 

 The conclusion seems justified that a brown spinel is rarely 

 if ever a constituent of a felspar-bearing member of the 

 Dundas series of plutonic rocks. This rule cannot be 

 applied universally, picotite or chromite may be present in 

 gabbro elsewhere. 1 



The structure of the rocks present some features of 

 interest. The grainsize is fairly constant, 4 mm. to 2 mm. 



1 Eosenbusch, Mikroskopische Physiographie der Mineralien und 

 Gesteine, 1907. Bd. n, t. i, p. 336. This distribution of spinels here 



series of ind ^ ■ un t Erebus series in the 



