16 Vi.1. XLIII., Art. 5.— T. Katö : 



resulting in a schistose structure in the rock as described above. 

 The mylonite, now under consideration, is one of the most charac 

 teristic products of the dynamic processes. 



In the course of driving the Myöjin tunnel which leads from 

 the village of Akénobé to Mikobata, it was found that a more or 

 less altered black slate (Paleozoic) constituted the west entrance of 

 the tunnel and was continuous for about 30 meters, giving place 

 to dioritic rocks, which form tlie greater part of the mountain 

 mass through which the tunnel was driven. The diorite collected 

 near the contact with the slate is light green and mottled in 

 colour, usually more or less greasy to the touch, and resembling 

 in some respects talcose or serpentinous rocks. Sometimes macro- 

 scopic distinction between this rock and the altered green slate 

 showing indistinct bedding planes is very difficult. 



Under the microscope, this rock is seen to have been strongly 

 mylonitized. It is composed of irregular -shaped grains of plagio- 

 clase and very pale green hornblende. The plagioclase belongs to 

 the oligoclase-andesine group and is characterized by very narrow 

 polysynthetic twin-lamellae, and often shows undulatory extinction. 

 It is usually mylonitized to a considerable extent. The margins 

 of the larger grains are crushed to fine grains (PI. IV., Fig. 1), 

 and, moreover, fissures and cracks through the larger grains are 

 filled with mylonitized grains. In places, the feldspar is entirely 

 crushed to very fine grains. The hornblende has also undergone 

 mylonitization, though not so intensely as in the feldspar. It is 

 often torn and bent, and in places crushed into minute grains and 

 fibrous flakes commingled with grains of feldspar. The hornblende 

 is occasionally altered to chlorite by later decomposition. Quartz 

 is present in varying quantities, always filling up the interstices 

 between the larger grains of feldspar and hornblende, and also the 



