92 HORN EXPEDITION — PETROLOGY. 



METAMORPHIC ROCKS. 



Gneiss. No. 76. Plate III., Fig. 1. 



This rock is somewhat foliated, which is not apparent in the drawing, as the 

 section was taken parallel to the foliation planes. Biotite is present in flakes 

 lying parallel to the foliation. The mass of the rock, however, is made up of 

 irregular interlocking grains of quartz, with some irregular grains of clear felspar, 

 together with a considerable number of idiomorphic and much decomposed felspars. 

 A considerable quantity of epidote is distributed through the mass in short 

 prismatic forms. This rock was obtained near EUery Creek in the McDonnell 

 Ranges. 



Fine-grained Gneiss. No. 192. Plate II., Fig. 6. 



Foliation is well marked in this rock by means of numerous parallel flakes of 

 biotite. The mass of the rock is made up of small grains of quartz and clear tri- 

 clinic felspar, with a certain amount of highly decomposed felspar. A colourless 

 micaceous mineral is present in small quantities, which is probably sericite. A 

 few large porphyritic grains of magnetite are scattered through the mass. This 

 rock occurs on the south side of Mount Conway in the McDonnell Ranges. 



Gneiss. No. 48. Sp. gr. 276. 



This rock contains a considerable quantity of a yellowish epidote. The 

 general texture is granulitic, with large porphyritic ciystals of pink microcline. 

 The mass of the rock is a granular aggregate of quartz and microcline. This 

 specimen came from Haast's Blufl'. 



Biotite Gneiss. No. 107. 



The constituents of this rock are biotite, triclinic felspar and some quartz, the 

 whole showing strongly-marked foliation, the felspar grains being elongated 

 parallel with the foliation. A small quantity of a pale rhombic pyroxene is 

 present, as well as numerous small prisons of apatite. This rock occurs between 

 Slip-panel Gap and Ellery Creek in the McDonnell Ranges. 



Gneiss. No. 206. 



Composed of a fine aggregate of quartz and felspar, a considerable amount 

 of the felspar being converted in places into epidote. Through the mass 



