22 ART. IJ. 15. KOTO : 



by what appears to have been the former action of thermal springs, 

 being characterized by a more or less bleached aspect of the rock 

 mass and by the change of the original color due to iron-oxide; 

 but in no case are the pyritic impregnations visible. It is un- 

 likely that any new store of workable ore-deposits occurs in these 

 spots, or at the point G, where the metam orphie schist, occurring 

 associated with limestone, contains some scattered grains of iron- 

 pyrite. 



D. Origin of the Ore-deposits 



From various facts gathered during his study of the mine, 

 Dr. Nakashima firmly believes that the origin of the ore-deposit 

 of Hol-gol was due to the action of underground thermal springs 

 which had a genetic relation to the basaltic eruption ^\ The writer 

 looking at the deposit from another standpoint, assigns it to the 

 category of contact-metamorphosed deposits. From the micro- 

 scopic descriptions of rocks given in the preceding pages, there is 

 no room to doubt the existence of contact-metamorphic phenomena 

 in limestone in the form of lime-silicate-hornfels, produced by the 

 intrusive action of the granitic magma that consolidated later to 

 form the mass of On-jin-san. In thin slides are seen ilvaite ^^ and 

 the sulphide ores. The latter, w^iich are believed to contain gold 

 exclusively, cluster on the spots where the calcite is replaced by 



1) See pages 18 and 24. 



2) There is another type of ilvaite or liëvrite. If we compare fig. 1 with fig. 2 in 

 PI. II., one cannot deny the existence of the two modifications of tlie same mineral. The 

 latter vthe right-hand figure) represents the normal acicular type; but the former an ab- 

 normal one appearing as if black iron ore is veiled in thin leaves of amorphous silica. In 

 dissolving the mineral, thin films of dirty amorphous gelatinous silica were left behind, which 

 look like the membrane in question. I am in doubt whetlier the membrane is of amorphous 

 silica or a lims-silicate. The latter is the more probable, as the membrane exhibits high 

 birefringency and extinguishes light parallel to the longer direction of the original crystal, 

 and s-how nagative character in the same direction. 



