38 ART '2. — B. KOTO: 



terrane of the west. At Sang-görl, a microgranitic-sphemlitic 

 porphyry ^^ appeared for a sliort distance with the phenocrysts 

 of quartz, orthoclase, and a very little biotite, and thence 

 onwards orthogneiss was seen. Whether the porphyry should 

 be regarded as a marginal faciès of orthogneiss or a later in- 

 trusion, it could not be decided. 



The change of rock is accompanied by a change of the 

 topography of tlie surrounding country. On the west we saw a 

 regular meridional ridge of the Hoami-tal-chld "^ pass (PI. IV. fuj. 2) 

 which was dislocated on the north by the equatorial ridge of Chin- 

 j'l/iL The former is built up of orthogneiss ''^ (the strike N. 20^E. 

 with the slope to the east, which is at the same time the schis- 

 tose plane of the rock (see ß(j. 1 ) ; the latter, the sandstone- 

 complex with fault scarp on the north. The line of this disloca- 

 tion runs through the CJiirl-mn massive to the west, as may be 



1 ) It is !i liglit-browD microj^ranitic rock in wLicli orthüclase, quartz and biotite, especially 

 tiie first two, are abundantly present so ns to give to the intnisive a giunular appearance. 

 Seen Tinder the microscope the microgranitic groundmass makes up half the bulk, while the 

 rest is composed of corroded quartz and idiomorphic zonal orthoclase, encircled by a fringe of 

 beaiitifiil spheriilite. It is macroscopically of (hagnostic moment to observe the thin lamellre 

 of biotite which appear like black rods. 



2) Ti -^ in.i^ 



'■)) A dark, chmitic;, half- schistose nv-'k in which the white feldspathose ground is striped 

 with black hornblenchc bands. Seen under the microscope it consists of a granular aggregate 

 of plagioclase finely twinned after albite and pericline laws. Between crossed niçois the lamel- 

 l;e of plagioclase are l)ent and exhiliit undulatory extinction, thus bearing testimony to having 

 been placed under stress without having been shattered to a cataclastic mass. Confused aggre- 

 gates of the shreds of grass-green hornl)lende and deep-brown biotite are strewn in bands, some 

 hornblende h(\aps being immersed in, and fringed with an accumulation of mica as if the latter 

 were derived from the former. Some zonally structured hornblende encloses a mass of whitish, 

 round or elongated mineral (epidote ?) in myrmeldtic fashion, and the biotite contains minerals 

 with the pleochroic halo. The former may appropriately be called the hornble7icle-m>jrineküe in 

 order to distingiiish it from the normal (cpiartz feldspar) leuromyrmekîle. The hornblende- 

 myrmekite is, so far as I know, confined to orthogneiss and the marginal facies of deep-seated 

 igneous rock. 



From the brief description given, we have here an ortho-dioritc-gneiss formed <lnring the 

 slow movement of an injection of viscous, intermediate-acid magma under the condition of 

 piezocrystallization. No qwirlz was seen. It is strange that the nx^k was found within the 

 ucidic gneiss terrane. 



