532 OGILVIE 



orthoclase, albite, oligoclase, titanite, apatite and quartz. In 

 some cases the dikes were but little metamorphosed, in others 

 they were intensely sheared, and there are all the intermediate 

 degrees of change. In the crushed varieties there is a pale biotite 

 poor in iron, associated at times with ordinary deep brown 

 biotite, at times with the orthoclase. The light biotite is 

 apparently secondary, of deep-seated or metamorphic origin. 

 Frequently the shreds of the secondary biotite are strung out in 

 lines having parallel orientation, giving the rock somewhat of a 

 schistose structure. In the crushed varieties microcline is com- 

 mon, as are undulatory extinction in the quartz, microperthitic 

 intergrowths and some granulation. A few crystals of zoisite 

 were to be seen, apparently derived from the plagioclase as a 

 product of dynamic metamorphism. Reaction rims are frequent 

 between the biotite and the hornblende. It is very common to 

 see a hornblende individual with deeply corroded edges sur- 

 rounded by a radiating mass of biotite leaves interspersed with 

 feldspar and dotted with magnetite, the whole enclosed in a 

 biotite individual. 



The feldspars, particularly orthoclase, contain inclusions of a 

 fine reddish black dust. Some mica is also present as inclusions. 

 The dust is to be seen especially in the central zones, the edges 

 being free from it. This type of inclusion is present in all the 

 rocks of the region. For reasons that will be discussed later 

 (see p. 538) these are thought to be titaniferous, and to consist of 

 several minerals notably perofskite, rutile, titanite and magnetite. 



Norm and Mode.- — -Plagioclase was the commonest mineral; 

 next in abundance, biotite and orthoclase in about equal amounts, 

 hornblende, augite and zoisite were in small amounts. It ap- 

 pears that the norm agrees fairly well with the mode. The 

 disagreements are that there is no anorthite (all the plagioclase 

 being near the albite end of the series) and no corundum, and that 

 the actual percentage of orthoclase is less than the normative. 

 All of these discrepancies are accounted for by the presence of 

 biotite, hornblende, augite and zoisite. These minerals are too 

 variable to admit of accurate recalculation, but it is evident 

 that some potash is in the biotite, and lime in the other three 

 with alumina distributed among them. 



