KAWA HYBRID ROCK. 135 



lying steeply to the W.N.W. Abundant rock is exposed on the 

 slope, but it is in a lumpy, boulder-like way, the rock being rounded 

 and weathered out into separate masses instead of presenting a 

 clean surface of continuous rock. 



This mixed basified acid rock has a striking appearance, being 



a coarse, dark and light, rock, glistening with 



Appearance and niin- l ar rr e poikilitic plates of biotite. Only two 



,ral composition. gpedmens were gathered of this rock, namely, 



2 -J\ (12514, PI. 16, fig. 5) from the locality now under description and fifo 



( 4 12515) from a short distance away to the north. Both are almost 



identical, but the first is coarser and consists of a fair amount of 



orthoclase, some scattered porphyritic crystals still remaining, 



abundant lath-shaped plagioclase (albite-oligoclase) and quartz, a 



fair amount of pyroxene in rather small idiomorphic and hypid.o- 



morphic grains, often gathered together into clusters and showing 



a change here and there to uralitic hornblende, a large amount 



of biotite in great ophitic plates, and, as accessories, iron ores and 



rather much apatite. 



If the above rock, as is suggested, is of the composite or hybrid 

 kind due to chemical reaction between the 

 Interpretation swg- tw0 roe j < bodies, such as a basifying of the 

 ■- ,sU>tl - granite or other very intimate mixture of the 



two rocks, it follows that whilst the quartz and orthoclase of the 

 oranite have remained, all the usually dominant microcline has 

 disappeared, and there results an abundance of plagioclase (albm - 

 oli^oclase) ; whilst the amount of biotite has been largely remiorced 

 and so also apparently that of the apatite. From the point of 

 view of the basic rock, the more basic plagioclase (labradonte) has 

 disappeared, as also has the olivine, whilst the pyroxene has 

 persisted in more or less patchy groupings. 



Except on the supposition of some such commingling of material 

 and chemical rearrangement having taken place, it is difficult to 

 classify a rock of such abnormal mineral constitution among the 

 ordinary igneous rocks. Its actual position in the section exactly 

 between the two supposed parent rocks, and the veming of it by 

 the basic igneous rock, are also suggestive. , . _ _ 



From the appended table of analyses made by Dr. Christie 



in which are shown the chemical compositions 



Chemical composition. ^ ^ spec j mens f the Kawa hybrid, that of 



the Kawa olivine-dolerite and that of the Kawa granite, side by 



