HORN EXPEDITION — PETKOLOfJY. 9o 



irregular patclies of secondary (juartz granules are (listril)Utecl, whieli seem to have 

 a somewhat parallel arrangement. Numeruus small Hakes of hiotite ai-e present, 

 as well as some small apatite prisms. The blown biotite is in part connect(!cl into 

 a green variety. This specinien eauie from the McDonnell Ranges between Slip- 

 panel Gap and Ellery Creek. 



Augen-gneiss. No. 4. 



This rock is of a basic character and allied to the diorites in composition, 

 quartz being practically absent. The " eyes "' consist of grains of triclinic felspar 

 with a little green hornblende, while the foliated groundmass is composed of 

 crushed fragments of felspar, dark brown biotite, and a little hornblende. ]:)esides 

 the above there are numerous pinkish-brown garnets and small grains of apatite 

 and zircon. This rock was found on the banks of Maude Creek, in the Hart 

 Range. 



Gneiss. No. 23. 



The bands of this gneiss ai'c composed of granules of clear felspar and a little 

 quai'tz alternating with layers of decomposed and fractured felspar grains. ^\^ pale 

 granular epidote is abundant, and there are a number of thin irregular flakes of a 

 white mica {sericite ?), which in places are aggregated into distinct bands. This 

 rock formed the walls to the quartz reef on the Wheel Fortune Claim, in the 

 Arltunga goldlields. 



Augen-gneiss. No. 249. Plate II., Fig. 5. 



The mass of the rock is made uji of closely coiiq.)acted "eyes," of fairly uniform 

 dimensions, and consisting oi grains of felspar mostly triclinic with a few grains of 

 quartz. Surrounding these "eyes" is a very perfect flow-structure formed by 

 strings of biotite altering into oxides of iron, and separated by layers of com- 

 minuted quartz dust probably mixed with secondary quartz. 



