Report on the Rock-Specimens. 323 



from Shap Fell, Westmoreland, with large pink porphyritic felspars. 

 The latter have a curious mottled extinction, and are probably to be 

 referred to microcline (moiree-niicrocline of Brogger) ; oligoclase, 

 with fine twin striations, is also present, with quartz, biotite, antl 

 a little brown hornblende. A pleochroic (pale rose to colourless) 

 sphene is fairly plentiful, while small apatites and zircons occur as 

 accessory constituents. There are also present one or two small 

 prismatic sections of a reddish-brown mineral, closely resembling the 

 Allanite described by Hobbs,^ in the granite of Ilchester, Maryland. 

 They have extinctions of 34°-37° to their length, and are pleochroic, 

 from reddish-brown along the line of extinction, to yellow at right 

 angles to it ; they show a zonal structure hexagonally round a 

 central nucleus similar te that figured by Hobbs. These characters, 

 as well as the strong refraction and weak double refraction, agree 

 with those of allanite (see PI., LI II., fig. 2). 



A biotite-hornblende granite from Geikie Land has no porphyritic 

 felspars, but in other respects is somewhat similar to the preceding, 

 and also contains allanite in small amount. The felspar is mainly 

 microcline, but some oligoclase is also present. Sphene occurs in 

 large amount, in some sections showing polysynthetic twinning. 



Another specimen from Geikie Land presents some of the 

 characters of an epidiorite. It contains biotite and much pleo- 

 chroic reddish-brown hornblende in large ragged plates, sometimes 

 surrounding a nucleus of colourless augite, with which it is in 

 optic continuity. The rock is much altered and contains kaolinised 

 idiomorphic felspars and some clear quartz ; a little calcite and some 

 needles of apatite are also present. 



A large granitic block from Possession Island is a garnetiferous 

 haplite with tourmaline, and is identical with the rock from Possession 

 Island in the lioss collection described in Min. Mag. XII., 79, and 

 also probably with the rock described as from Cape Adare in Proc. 

 Eoy. Soc, N.S.W., XXIX., 471. 



PLAGIOCLASE-OLIVINE-AUGITE-BIOTITE ROCK. 



A small rolled pebble, probably from Cape Adare, has the 

 aspect of a gabbro, and shows in a ground of clear colourless 

 prismatic felspars dark patches of ferro-magnesian minerals, amongst 

 which olivine and biotite are conspicuous. Under the microscope 



1 Ann. J. Sci., XXXYIIL, p. 223, 1889. 



Y 2 



