ROCK SPECIMENS FROM CENTRAL AND WESTERN AUSTRALIA. ^99 



lie in characteristic forms, clinozoisite and sphene in 

 granules, actinolite and chlorite in more or less elongate 

 prismatic forms. There are in addition a few nests of 

 secondary quartz and epidote, while the veinlets are seen 

 to consist of clinozoisite with a little sphene. The rock is 

 a fine grained amphibolite, rather more felspathic than 

 usual. 



Rocks very similar to this are of frequent occurrence in 

 thegoldfields of Western Australia, e.g., Kalgoorlie, Norse- 

 man, the Murchison Valley, etc. They seem to form the 

 country into which large dykes of coarse grained basic 

 rocks, now also amphibolites, have been intruded, and may 

 therefore be termed the older amphibolites. As a rule 

 these fine grained amphibolites are not conspicuously auri- 

 ferous, except near the contact of graphite or quartz- 

 porphyry. The specimen, however, is of considerable 

 importance in showing that the rocks of the known aurifer- 

 ous belts are found as far eastwards as the Cavanagh Range. 



The remaining rocks are probably intrusive, though the 

 interpetation of some is not without doubt. A rock from 

 Skirmish Hill (22/7/91) is probably to be identified as a 

 much altered quartz porphyry. The hand specimen is grey- 

 black and aphanatic except for red phenocrysts of felspar. 

 In section these phenocrysts are excessively turbid, but 

 may be identified as orthoclase in many cases, although an 

 acid plagioclase also appears to be present. Apatite occurs 

 in large prisms of such size as to deserve the name of 

 phenocryst, and magnetite also occurs in large grains. 

 Much more abundant than the felspar is quartz, in very 

 perfectly elliptical shapes. Sometimes these are occupied 

 by one large plate of quartz, with a marked rim of dusty 

 inclusions at a short distance from the margin, or a mar- 

 ginal fringe of small grains, at other times by a mosaic of 

 grains of smaller size. Though bearing much resemblance 



