THE ARCHiEAX FORMATION OF THE ABUKUMA PLATEAU. 203 



Next ooine.s a peculiai-, ])l:ir'k vock (P Y), of iniissive appearniice 

 and more or less schistose in structure. It is almost entirely marie 

 up of large horîiblende-individuals witli some traces of feldspar and 

 angite. This is evidently part of tlie gabl)ro-diorite, crushed and 

 compacted to the present form, and accompanied by a new formation of 

 hornljlende, wliicli occurs in lenticular spaces with tolerably perfect 

 crystallographic outlines. How this is related to the diorite is as yet 

 nidviiown to me. If tliis relation were thorougldy examined, 

 some light might be thrown on the genesis of schistose horn])lende 

 rocks, whi('li are of wide distril)ution in Aljukuma and elsewhere. 



The gabl)ro diorite re-appears from Yöjigata as far as the place 

 called Hirasode, interrupted at its middle by a- mass of hornblende- 

 gr:inite. On ascending the Hanatate pass to Saimarii, we see 

 ao'ain the hornblende-o^ranite, often containino- detached masses of 

 titanitediornblende schist' and also sniaJ) fragments of it (marked 

 X in the profile), which produce the appearance of a breccia, cemented 

 by a granitic material. The whole is frequently traversed ])y yel- 

 lowish, fine-grained aplitic or pegmatophyritic dykes. The included 

 ampliibolite dips towards jST. E. with the strike of X. 45° W. 



We tlien proceed westward from Saimaru, tlirougli a tliickly 

 wooded, steep ascent of the Nakayama, pa,ss, locally known as " Xaka- 

 yama 8anri," and finally come to tlie top, beyond whicli an interest- 

 ing series of the Archœm schists may be seen. It is mainly an 

 alternation of (a.) the titanite-hornblende schist, (h) mica-schist, and 

 (c) gneiss-mica schist ; the second often a,ppro;iching both in its com- 

 position and appearance to a true quartz-schist in losing either biotite 

 or muscovite. The whole complex is included by the present writer 

 under the Tahanuhi series, and considered l)y him to be the oldest 



• This is the rock that largely enters iato the cooaposition of the upper horizon of the T.ika- 

 nuki series. 



