THE ARCH^AX FORMATION OF THE ABUKUMA PLATEAU. 257 



brown tf) grey ; but some drop-like grains are highly chromatic and 

 have a striking similarity with the olivine grains which are also said 

 to be found in some amphibole-bearing schists. Prof. Kalkowsky^ 

 has mentioned the occurrence of olivine grains which ckister I'ound the 

 ir(3n-ores, iunl the figures of the olivine (glinkite) given htj him have a 

 I'emarlahle similaritg with the above-mentioned grains of titanite with the 

 enclosed titani ferons iron.' 1 have, tlierefore, some doubts as to the 

 real nature of the present titanite, and consequently have had it 

 subjected to a chemical examination which proves the presence of 

 titanium in it. 



The titanite grains in the basic, hornblende zones mostly possess 

 black cores, and the minerals which accompany such titanite are 

 biotite and hornblende, b(jth being ferriferous components, while 

 in the acid, salite band the grains are usually /;Y'(;/rom the black iron- 

 ore. The first modification of titanite may be fairly compared with 

 the so-called titanomorphite, resulting from the decomposition of the 

 titanic iron ; Ijut in the present case I can not conceive the titanite- 

 margin to be derived from the black core ; they are original, and 

 should not be taken for titanomorphite. 



The hornblende in the salite-band is pre-eminently green and 

 pleochroic ; the feldspar is one of the striped varieties. There is also 



1 Die Gneis.fformation des Eulengehirges, p. 37-38. See also Dr. E. Dathes work: 

 Olivinfels, Amjjhiholit und Biotitfjneiss von Habendorf in Sclde^ien, in the Jahrbuch der königl. 

 preuss. geologischen Landesanstalt für 1888, p. 322-324. The amphibolites of the gneiss 

 formation of the Eulengebirge seem specially rich in the olivine grains, as may be judged from 

 Kalkowsky's and Dathe's work. So far as I know, I have as yet not come across the olivine in 

 any of the genuine amphiljolite-schists of Japan. The peridotites and serpentines, however, 

 often contain that mineral ; but they occur only in the form of intrusive bosses, sheets, and 

 dykes in the archsean memljers. 



2 Mr. J. J. Harris Teall has given a s-iniilar figure in Plate XLVII, fig. 3, in his " British 

 Petrography " with a note that it " shall rei:)resent a kernel of iron ore zoned by sphene." 

 Unfortunately he was obliged to postpone all detailed references to this mineral to some fixture 

 occasion, notwithstanding the fact that the plate had been prepared of a glaucophane-schist 

 from Anglesea, in which the above-mentioned titanite is said to occur. 



