312 B. KOTO: CAUSE OF THE GREAT 



mon, the Gate of Corca, sitnatcd at tlic sijutb-east coi-nev of Liau-tang. 



,?) Hornblende-porphyry. — This is a hovnblende-diorite-porphyritc, of an 

 ashy-looking aspect, with tolerably large (üinin.), Avcll-tlefined crystals of honihh'iidiiiH 

 the povphyritic ingredient, seemingly forining dykes in the Palicozoic complex. The 

 general mass is a greyish, tine-crystalline aggregate, in which no other component 

 except the above-mentioned hornblende is to be seen. The anjphibole-phenocrysts 

 arc of two varieties ; the one is in well-defined prisms of compact texture, with the 

 clcavcige face porfejt and sluwing a sub-metallic lustre ; the other is rather greenish 

 and fibrous with imporfe^-t crystallographic outlines. The distinctive features of the 

 two become more pronounced, when viewed under the microscope. 



The compact hornblende is of a deep-brownish colour with dili'ereut tones in 

 centre and peripher}', and is bordered by greyish and blackish granules of 

 li'iicoA-c'iic. Its pleochroisin is distinct ; its outline is tolerably regular, and twimied 

 in that shape which was formerly considered as anomalous twins whose plane of 

 contact was supposed to be the prism goP 2 (120). i The other variety is of a 

 yellowish-green, line, parallel-librous texture, resolving oftentimes into chloritic 

 patches. A large (quantity of magnetite is present, being scattered through the 

 Avliole mass. 



The rest of the rook is holocrystalline, being built of lath-shaped fehhjxir, 

 chloritic honihleiuh; and black iron-ore with borders of leucoxcne. The greyish, more 

 or less decomposed feldspar is simply or doubly twinned. There seems to occur 

 another feldspar Avhicli is of rather larger size than the other, and of irregular 

 outlines with no signs of a twinning structure. It is probably orthoclase. Allo- 

 triomorphic angular i/Kart: fills up the interstices left by other ingredients. It is 

 present only in small (juantity, and shows a greyish tinge between crossed niçois 

 with undulatory extinction. The c[uartz contains abundance of li(|U id-inclusions with 

 spontaneously mj\ing bubbles. The general colour of the ground-mass is grey, on 

 account of the presence of a large ainjunt of leucoxene and chloritic matter, with 

 an aggregate of more or less decomposed, greyish feldspar. 



As ni:iy bi3 seen i'roiii the sketch in i*lule XÄX., tlie strike of the 

 PiiUeozoic form.itions changes its direction in a mo;-;t peculiar manner. 



t Becke ; T^icheraiak's miuoralu^-. nud peirogT. Mittli. Bd. IV, p. 305. 



