. ANTARCTIC ROCKS AND MINERALS. 41 



much better developed than usual, and exhibit good 

 crystalline outlines, high refraction, straight extinction, 

 and an irregular cleavage transverse to their length, and 

 somewhat similar to that exhibited by the Fayalites 

 in the Sandy Bay Basalt. Fig. II. diagrammatically 

 represents a section of this rock. The olivines are only 

 slightly decomposed. Magnetite sometimes forms 

 peculiar skeletons (perhaps decomposition products of 

 the olivine), one of which is represented in Fig. III. 

 The section of this rock is too thick to admit of an 

 accurate determination of glass in the base. 



Of the Sedimentary Rocks we have a single represen- 

 tative, in the form of a sandstone, fine-grained, and com- 

 posed of angular fragments of felspars. 



Amongst the altered rocks there is one specimen of a 

 grey schistose rock Avhich, under the microscope, in 

 transmitted light, shows a confused mass of transparent 

 flakes (perhaps sericite), with here and there large spots, 

 probably occupying the place of former crystals. 

 Analysis shows this rock to consist chiefly of SiOj, 

 Fe2 O3 (or Fe O), and Al^ O3, with traces of Ca O, and 

 a high ignition loss of 5 "45 per cent. This would point to 

 a rock from which K2 O, Na^-O, MgO, and Ca O had 

 been leached out, and secondary hydrous compounds 

 formed. This analysis agrees with those given by 

 Rosenbusch (Elemente der Gesteinlehre, p. 497), and 

 points to a rock of continental origin, and along with the 

 Biotite Mica Schist of Professor David's collection, 

 gives strong circumstantial evidence as to the existence, 

 at some time, of an Antarctic Continent. 



The remaining specimen is of a brown-red colour, and 

 slightly scoriaceous, and, most probably, is a decom- 

 position product of some scoriaceous basalt. 



The authors, in conclusion, wish to thank Mr. Morton 

 for the kind loan of the above specimens ; and also Mr. 

 W. H. Twelvetrees, for some kindly hints. 



