THE PETROGRAPHY OF JAVA AND CELEBES 239 



freshness of these rocks along the roadside where not covered by 

 soil and vegetation is extremely interesting and was unexpected, 

 since the rocks are intrusive bodies which have been uncovered by 

 gradual erosion, and are not recent lava flows. They consist of 

 abundant crystals of black mica, the largest 4 mm. in diameter, 

 with euhedral prisms of augite, the largest being 6 mm. long, 

 besides nearly equal amounts of glassy feldspar, some of which 

 is prismoid, while others are anhedral. In thin sections these 

 rocks are seen to consist of nearly equal amounts of mafic minerals 

 and feldspar, which are augite, much brown biotite, considerable 

 magnetite and apatite; the feldspar is almost wholly orthoclase 

 in prismoid sections, with very little lime-soda feldspar. One 

 section shows a little interstitial quartz. 



Similar varieties of shonkinite occur as bowlders in the stream 

 Gentungen. One variety at this locality is very similar in general 

 appearance to those just described, but is richer in mafic minerals. 

 It is medium grained, in thin section it might be called coarse 

 grained, and consists of much augite and brown biotite, which 

 crystallized almost synchronously and inclose much colorless 

 apatite, and also magnetite. There is also a very small amount 

 of greenish hornblende which has crystallized around augite. 

 The subordinate felsic components of the rock are chiefly ortho- 

 clase, or microperthite, which is slightly cloudy, besides some very 

 transparent calcic plagioclase, and a small amount of interstitial 

 isotropic mineral which is probably sodalite. The chemical com- 

 position of this variety of shonkinite is shown by analysis No. 16, 

 and its place in the Quantitative System of Classification is found 

 to be in division III. 6. 3. 2, ottajanose, more exactly its symbol 

 is III. 6. (2) 3. 2. The norm contains over 10 per cent of lenads 

 and 12 per cent of olivine which do not appear in the mode, owing 

 to the large amount of biotite which crystallized from the magma. 

 This variety of shonkinite has been called marosite. 



Still another variety of shonkinite found in bowlders in Gen- 

 tungen is characterized by large poikilitic micas, 20-30 mm. in 

 diameter, which lie in all possible positions in the rock. This 

 variety grades into one in which the micas are not poikilitic, but 

 yield brilliant cleavage plates 10-15 mm. in diameter. In thin 



