THE ARCH^AN FORMATION OF THE ABUKUMA PLATEAU. 9,37 



surrounded by accumulations of tlie epidote grains ; the peripheral 

 portions are chloritized, leaving cores of the hornblende in the centre. 

 The secondary epidote occurs fringed with chloritic fibres, and this 

 general distribution of the green minerals causes the rocks to appear 

 of a dark-green shade. The large well-defined crystals of mngnetite 

 are newly f<:)rmed ; the small crystals of it are heaped together in 

 the spot formerly occupied by the m agnesium-bi silicates out of which 

 they have been formed. The leucoxene mineral encircles the rounded 

 magnetite, from which it may be inferred that the iron ore is 

 titaniferous. The quartz is darkened and clouded with an immense 

 accumulation of liquid-inclusions, arranged in bands along the fissures 

 and cracks. 



As to the feldspar it is for the greater part kaolinized, especially 

 in the central portion ; the periphery remains comparati\'ely in an 

 unaltered condition ; the original shell-structure and the chemical 

 difference in the zoning thus become ap|)arent ; the peripheral portions 

 of the crystals display weak polnrization-colours. Some feldspars 

 appear homogeneous by simple transmitted light ; but after applying 

 crossed Mcols, twinning structures are well exhibited by different 

 colours in alternate h".mella3 ; and, moreover, extremely fine lines are 

 developed just across the twins of tlie first tvpe. These second twins 

 do not extend over the whole breadth of the lamelloä, but are usually 

 only partial, being very abundant along the twinning plane of the 

 albitetype. The feldspar, apparently of an orthoclase nature, is, tliere- 

 fore, really microcline, having the characteristic cross-hatching struc- 

 ture. Where feldspars come in direct contact with the chloritized 

 biotite, a zone of accumulation of epidote grains occurs in the substance 

 of the feldspar, around the altered biotite, in such abundant quantity 

 as to make that portion appear quite dull. The feldspar itself appears 

 at first sight simple and homogeneous, but when viewed by polarized 



