262 ^- ^oTö. 



I begin with the lower nieml)er, a highly crystalline amphibolite. 



a) It is a schistose, im) perfectly fissile, evenly plane-parallel, dark- 

 green, slatv rock, built up of multifarious alternations of white and black 

 bands, comprised of microscopically fine, glittering needles of a black 

 hornblende and saccharoidal, milky-white feldspar, disposed, as I have 

 stated, in fine zones. Sucli rocks diifer so little from those of the 

 Takanuki series in their external appearance as to lead one to 

 suppose them to be quite identical. However, on close examination 

 marks of distinction may be easily perceived. For besides the fineness 

 of texture which characterizes the present rock, the spangling gold-gellow 

 hiotite can not he seen on weathered surfaces of ü as on those of the titanite- 

 aniplnholite^ ; these surfaces are dark-green and dull. 



Under the microscope the hornl^lende ;ip])ears compact, and 

 with irregular outlines, and als(j in ragged plates which are 

 either short and ol)long, or have tlie shape of slender prisms. The small 

 prisms are arranged more or less parallel. The broader plates are 

 less parallel, crossing e;ich other at various angles, and giving a 

 coarsely felted aspect to the section. In the plates very fine 

 striations run parnllel to the base. As all the crystals of the horn- 

 blende are not disposed in ])ârallel direction, so basal sections are 

 sometimes observed in tlie combination of prism ntid clinopinacoid. 

 The mineral is of a dirty-green colour, and pleocliroic, varying from 

 green to oily-yellow. The general mass is made up of feldspar (and 

 some quartz?) with crystalloids of hornblende. The feldspar is not uni- 

 form in size, and is polygonal in outline ; its polarization-colour is 

 weak, showing undulatory concentric extinctions ; its substance is clear 

 and fresh. Only a few flakes of hiotite are to be seen on the cleaved plane. 

 Microscopically the biotite may be considered as an accessory, occurring 

 associated with the hornblende aggregates as brown, fibrous lamellae, 



1 See ante p. 251. 



