224 



B. KOTO. 



pierce tliroiigh the «ubstaiice of hornblende and l^iotite, and partictdarly 

 int(j the grains of feldspar enclosed by the horn 1>J en de of the canght-up 

 granite. The larger apatite-crystals are short and broad, and have 

 the edges rounded perhaps by corrosive action; the delicate, slender 

 needles of the same mineral are sharply bounded by plane surfaces with, 

 h(3wever, broken terminations, and are comparatively small in 

 size. At tirst sio-ht, both modifications seem not to be of identical 

 chemical composition ; Ijut their respective cross -section s give the cine 

 to their true nature, and show that both modifications belong to the 

 same mineral. The well-defined needles may l}e of a later origin, and 

 their formation may be ascribed to the effect of a contact metamorphism. 

 The magnetite is sparingly present in the normal rocks, but in the 

 schistose variety and also in the patches caught up by biotite-granite, 

 it is plentiful, occin-ring either in a drop-like form, or in well- 

 finislied octahedrons. Iron j)ijrites forms part of clumps of magnetite, 

 and performs the function of the interstitial mass between the granitic 

 components, just like the mesostasis of younger eruptives. The octahe- 

 drons of magnetite are specially abundant within somewhat 

 decomposed feldspars. Also in a partly altered hornblende, the same 

 mineral fills up the clefts of cleavage-planes, appearing just like 

 numerous black needles, all regularly arranged ])arallel with the princi- 

 pal axis of the crystal. As a whole, the formation of the magnetite 

 seems to stand in intimate connection with the act of inetamorphism. 

 The deposit of magnetite in the valley of Clu'ika makes its appearance 

 between the diatrophic clefts of a strongly compressed gneissose ov 

 schistose hornblende-granite, and the source of the iron ore must be 

 souo"ht for as similar to that of the formation of magnetite in the <''ra- 

 nite, already referred to. iSometimes blood- red tablets of iron -glance 

 are interposed in feldspars with a certain definite arrangement, appear- 

 ing in black needles and in minute red scales, producing thereby the 



