10 



Iwasaki : 



contact with limestone, magnetite lamolke, perhaps flattened 

 rhombic dodecahedrons, are seen projecting from the porphyrite 

 into the hmestone (Fig. 1 and Fig. 2). While the porphyrite 

 was in the deep as fused magma at high temperature, it was a 

 eutectic compound with the iron content uniformly diffused 

 throughout. But Avhen the magma Avas erupted and came into 

 contact with the limestone, its temperatm-e fell and its chemical 

 properties became entirely different from those it had in the deep. 

 Magmatic differentiation took place at the niargin of the magma. 

 Magnetite was driven out of it to form the thick deposit between 

 it and the hmestone, ^y[nch finally attained a thickness of 30 feet. 



The arrangement of 

 minerals in this contact 

 deposit is highly instruc- 

 tive as to the order of 

 the petrification of emana- 

 tiojis (Fig. 3). Magnetite 

 is found on the side of the 

 diorite-porphyrite, garnet 

 constituting the central 



A B C D E F , T 



■^. „ . , , , . , zone comes next, and 



Jig. 3 — Arrangeirent or ii.merals in the contact deposit 



of the Kamaishi Mine. A, Dioriteporpyrite. quartZ OU the sidc of tho 



B, Magnetite. C, Garnet. D, Quartz. limCStOUe. lu the qUartz, 



E, Cakite with gold. F, Limestone. ... ,, t 



calcite masses are scattered 

 about, and in them the gold is remarkably rich. The gold grains 

 are usually microscopic, being sometimes as large as ] cm. 

 in length, and 0.2 cm. in diameter. They are of two kinds. 

 One is like granulated zinc in form, and is supposed to have 

 been solidified from the fused drops of gold in the liquid 

 emanations exuded from the diorite magma. The colour of the 

 gold is very fine being almost like that of pure gold. The other 

 kind of gold is always in long prismatic crystals, acutely pointed 

 at both ends. These are perhaps rhombic dodecahedrons, elong- 

 ated on an axis. They are paler in colour, are found in the 

 cleavage of calcite, and are supposed to be of secondary origin in 

 contrast with the former, which are of primarN' origin. 



