MR. T. H. HOLLAND ON ROCK-SPECIMENS FROM KOREA. 187 



CB'i'h with a high, refractive index, strong double refraction, and 

 wide extinction-angle. These granules, so far as it is ])ossible to 

 determine, present all the characters of the granular augites of the 

 matrix. Quartz crystals zoned around in this manner in the 

 magma were mentioned by Prof. Zirkel as occurring in some augite- 

 andesites of Arran *. More recently J)r. Hatch has observed similar 

 sporadic quartz-crystals in some specimens collected by the llev. 

 Mr. Baron in Madagascar t. 



Secondary quartz and chlorite occur in this rock. Magnetite 

 exists in abundance. The high powers of the microscope reveal the 

 presence in the matrix of a series of yellow-brown pleochroic 

 crvstals of (probably) hornblende. 



'a rock having a specific gravity of 2*73, from a river-gorge near 

 Chhungdo, presents, in the hand-specimen, characters similar to the 

 foregoing example. It is dark-green and compact, with an abun- 

 dance of stout prismatic crystals of plagioclase, which, with augite, 

 form the principal porphyritic constituents. As shown by their 

 extinction-angles, the felspars vary in chemical composition from 

 labradorite to bytownite. The crystals are frequently split along 

 the gliding-planes with intrusions of the magma. The augites are 

 partly converted into hornblende, with bye-products of epidote and 

 chlorite. Iron oxides occur as granules of magnetite, and as smaller 

 flakes of red hydrated products, scattered through a grey matrix of 

 closely felted plagioclase-microliths, exhibiting a fluidal arrange- 

 ment. The structure presented in the matrix of this rock is similar to 

 that to which Eosenbusch gave the name " pilotaxitic " t, and might 

 have been at one time hyalopilitic. This rock presents many of the 

 appearances of the true andesites or propylites ; in fact, the majority 

 of the specimens obtained from the south-east of Korea exhibit 

 characters bordering on the augite-andesites, propylites, and basalts. 



In an andesitic rock from Pumasa, we have examples of the com- 

 plete uralitization of augite. In addition to these, some of the 

 crvstals, whilst retaining the cleavage, form, and twin-structures 

 characteristic of augite, exhibit the peculiar pleochroism of horn- 

 blende. A separation in lines of dusty magnetite fre(]uently 

 characterizes the uralitic crystals. The large plagioclase-felspars 

 of rather a basic type are rendered cloudy in appearance by the 

 inclusion of a very fine, black dust, the particles of which are 

 scarcely capable of distinct individualization even under high powers 

 of the "^microscope ; and, although frequently occurring arranged 

 along irregular, curved lines, they sometimes occur in rectilinear 

 hands parallel to the twin-planes. From the way in which they 

 follow in intensity the zoning of the crystals, they present the 

 a])pearance of being original. Dr. Hatch mentions the occurrence 

 of similar dusty inclusions in the felspars of a Malagasy olivine- 



* * Geologlsche Skizzen von der Westkiiste Schottlan Is,' Zeltschr. Deutsch. 

 geol. Gesellsch. vol. xxiii. (1871) p. 23. 



t Quart. Journ. Geol. Soc. vol. xlv. (1889) p. 347. 

 + 'Mikr. Phvs. mass. Gest.' 2ik\ ed. p. 400. 



