THE ARCH^AN FORMATION OF THE ABUKUMA PLATEAU 285 



These pathological varieties, so to speak, which go by the current 

 name of gneiss-granite or granite-gneiss, though very improperly, 

 are, no doubt, mainly dynamo-metamorphic products. Microscopic 

 analvses give at any time sufficient proofs of their having been atfected 

 in the wav indicated. My own detailed study of them shows that 

 the first inducement to the schistosity of granites is to be found in 

 the sliglit shifting in ]josition of the ferro-magnesian silicates, and 

 in the commencement of granulation in the solid ([uartz. In a 

 more advanced stage of schistosity as in :2), ordinary schistose 

 o-ranite. all essential comj^onents have been compressed into deformed 

 bixlies ; tlie once evenly lamellar biotite altered into flexuous and 

 wrinkled lamelhr with bird's-eye-maple shimmer ; the hornblende 

 no longer of a ])rismatic form ; and the cpiartz and hornblende 

 rolled out and grained and compacted into one mass with a feldspar 

 centre zoned by the grains of quartz, thus simulating the so-called 

 centric structure by migration of the graiuilar (piartzes. In the last 

 phase of transformation as in 3), the schistose epidote-granite, the 

 horn])lende has disappeared entirely, being replaced by a mass of epidote 

 and magnetite. The biotite is bent and frayed out at the margins. 

 Heterogeneous aggregates, consisting of epidote, magnetite, and 

 chloritic matters, form wandering zones. The feldspar, the most 

 enduring mineral, escapes the general disintegration and granulation, 

 excepting in its peripheral portion, where the crystal is crushed, 

 producing the cataclastic structure. In spite of the solidity of quartz, 

 this has always been the first to yield to pressure. 



The cause of the schistosity is undoubtedly dynamo-metamorphic. 

 Extensive rendings and foldings hav<e taken place in the Abukuma 

 plateau only at the marginal zones, while the central height has 

 remained quite intact. V)y the orogenetic, diiferential movement thus 

 produced, the east and west side of the plateau have been thrown 



