bEOLOGY AND OEE DEPOSITS OF SU-AN 13 



obliquely to the sides, and these may belong to either tlie icositetra- 

 hedron or the topazolite type. Interference-colors range from grayish- 

 blue to yellow. The optic axial plane, though faintly indicated, cor- 

 responds to the longer diagonal of the rhomb. The rhomb itself, as 

 seen orthoscopically, consists of two pairs of optic fields limited by the 

 diagonals, extinguishing light symmetrically at about 4° with reference 

 to the shorter one. 



The andradite encloses diopside when botli occur together produc- 

 ing a poicilitic structure, and the polygonal interstices are fi,lled with 

 calcite ^\ Then the rock has microscopically an appearance like that of 

 eclogite, the ground of brownish-red garnet being speckled with greenish 

 augite. 



There is a trapeziforin mineral in the slide witli the color and 

 pleochroism of schorl. Extinction is always oblique. It is probably a 

 triclinic mineral resembling axinite, though the latter is never reported 

 to occur in twins The problematic mineral is frequently twinned with 

 its suture-line corresponding to tiie longer diagonal of trapezium, and 

 extinguishes light symmetrically at about 20° with reference to that 

 trace of the twinning plane. If the mineral be assumed to be axinite, 

 the twinning plane should correspond to (010). 



The preceding complex (a-e) was tilted and dislocated to its 

 present position, and was later intruded by eruptives, of which the 

 following play important rôles. 



/) Porphyritic hornbiende=granite. (PI. III. fig. 4.) 



Composition : Essential: Orthoclase, oligoclase, quartz, 

 green hornblende, biotite. 



1) This fact may be attributable to a decrease of molecular volume during crystallization 

 of the original limestone, and to a later importation through some channel of chemical 

 substances from the exudation of cooling granitic magma in a liydro- thermal way. Then, by 

 recombination and crystallization were formed many microscopic drusy lioles which are later 

 filled with calcite. 



