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fl.s large a mimher as the pegmatophyre clißes. Pegmatites are usually 

 considered as an accidental, mineral aggregate, deposited from solution, 

 by lateral secretion. If we view our pegmatite from this stand-point, 

 its formation must be ascribed to an origin entirely different from that 

 of the pegmatophyre dykes, in spite of close resemblance in their mode 

 of occurrence, structure, and mineralogical composition. 



My trip to the Abukuma district had for its scope to establish, if 

 possible, the stratigraphical sequence of archoean rocks, the study of 

 which has been long neglected by us, and which no one had attempt- 

 ed to follow in detail. Keeping always in my mind this import- 

 ant question, I had no time to avail myself of opportunities to make 

 observations on dykes in general, and I am at present not able to say 

 anything definite about the relation of the pegmatite and pegmatophyre 

 diikes. At the time I simply considered them to be all of one and ihe 

 same origin, which in renlity cannot be the case! 



Thetrue pegmatite may be best studied at Ishikawa-yama, 2 km. 

 north of Ishikawa, where Kochibe had found a crystal of beryl in the 

 newly exposed dyke on the road- side. Large orthoclase, twinned on 

 the ]>aveno type, and equally large and well-shaped, grey quartz, pegma- 

 tically intergrown with the former, together with biotite and muscovite, 

 form the materials of the coarse dykes. Beautiful dykes of graphic 

 granite with biotite may also be observed at Gomisawa, 12 km. east 

 of Ono-niimachi. Microcline seems to form an important part among 

 their components. These and many other dykes, of which there 

 are ample variety, require more extended researches than I had time 

 to institute. 



B. Dyhes of Aiigite-dioritic Lamprophyres. 



A dyke of about 2 m., cutting through hornblende-granite, is 

 found in Nishiyama (Ogura), on the way to Tanagura. It is a 



