THE ARCH^AN FORMATION OF THE ABUKUMA PLATEAU. 259 



B c) Titanite-Feldspar-AmpJtibolite. 



This approaches in its (mtward appearance to the first variety, but 

 it ma}^ lie reidily distingui.shed from the mica-bearing- amphibolites by 

 the absence of biotite. Also for the same reason the plane-parallel 

 structure, which is macroscopically observable in all hand-specimens 

 when the biotite is present, is not perfectly developed; the cross-section 

 is, hovve\'er, fine-banded, owing to repeated alternation of the Avhite 

 zones of feldspar with the black (jnes. The feldspar and hornblende are 

 nearly of the same size, and are fine when comj^ired with the two 

 preceding modifications. 



The hornblende is grass-green and pleochroic, bacillar in form, and 

 is arranged approximately in parallel directions ; the feldspar is clear, 

 and polygonal in outline. The particles (^f the latter are minute and 

 granular in the wliite zones, and the titanite-grains, occurrino- with 

 them, with their usual black cores, are chained one ai'ter another, parallel 

 to the banding of the schist. Weathered rocks look not rnilike a 

 sandstone-mass. The sjjecimens examined are those from Sori near 

 Ishikawa. and Yamagami near Matsukawa. I sa\v some traces of 

 copper pyrites in them. 



B dj Biotite- Amphibole-Gneiss. 



This occurs in the titan ite-biotite-amphibolite as a lenticular mass 

 of scarcely half a metre in breadth, and can be easily distino-uished 

 from all others of the present series by a fine granular-lamellar structure. 

 A transversely fractured block shows in the cle:u-est manner the mode 

 of aggregaticjn of the comp.ments. The black, flame-shaped, patches 

 are nothing but granular accumulations of a greenish-brown, bacillar 

 hornblende with traces of the basal cleavage, and the white dots are 

 porphyritic, untwinned feldspars, nearly all completely changed into a 



