OQ AKT. 2.-— B. KOTO: 



the feldspar of the orthochise-qnartz matrix lias been removed by 

 decomposition leaving; hollows and prodnciuy; thereby a grayish 

 pumiceoua aspect. Besides, the pîagiœlase-phenocri/si abont 5 mm in 

 size has also been weathered away prodncing round depressions on 

 the altered surface of the rock. There are also a very few macroscopic 

 patches of quartz whijli, of course, resist atmospheric decomposition. 

 By the simultaneous and p3rfect crystallization of Ijotli the orthoclase 

 and the quartz, which are present ia approximately equal quantities 

 and sizes, the comparatively idiomorphic, isometric orthoclase *', scattered 

 in different directions, is soldered together by the quartz of a some- 

 what later crystallization. 



Seen under the microscope, the form of both components, 1 mm 

 in size, is polygonal, and the structure interlocked or implicated. The 

 quartz, however, shows optical continuity extending through several grains, 

 so that the mineral must be regarded as a plate in whicli the orthoclase 

 is imbedded. It is therefore the ant i peg mat If Ic and not tlie normal 

 pagmatitic structure, for in ths latter the ortho-îlass serves as the 

 base. 



Another pecuHar feature is the exclusively plagioclastic nature of 

 the feldspar-phenocrysts of indefinite outline, gradually merging into 

 the general mass, the myrmekitic intergrowth of it Avith the quartz 

 being seen only at the peripheries of the phenocrysts. Sometimes I 

 found patches of quartz in Avhich the rudely vermlctdar orthoclase is 

 disclosed by the staining method, contrary to the usual habit of the 

 formation of the qmrt^. vermiede in granophyres. 



The only other component is a little biotite. The orthoclase in the 

 general mass is all kaolinized, Init, as I have stated above, the 

 plagioclase-phenocrysts are quite fresh and pure, though peculiarly 

 traversed by numerous clefts, and therefore' having a fritted appearance ; 

 the consequence being that the feldspar of the general mass and the 

 phenocrysts, the latter on account of their friable nature, are easily 



1) In acid rocks the urtboclase is nearly equiilimeasional. 



