110 R. A. Farquharson — Petrology of N. Kalgoorlie, 



it becomes a useful corroborative criterion in the interpretation of 

 previous hydro-thermal high pressure conditions. It has been 

 observed to be always a secondary mineral not adjusted to the belt 

 of weathering. The mineral develops typically by hot spring 

 action. . . ." 



Further, in his description of the rocks of Cape Colville Peninsula, 

 IN^ew Zealand,^ Professor Solias describes specimens that were sent 

 to him from localities very rich in rocks of andesite and porpliyrite 

 character as quartz-sericite rocks of indeterminable origin. If it is 

 borne in mind that tourmaline is quite prevalent in the North End, 

 except in the lodes, and that its formation is generally held to be 

 due to solfataric or pneumatolytic action, there appears at least 

 a possibility that the specimens are the altered product of the quartz- 

 keratophyre rock. 



Again, in some instances, no clear line of demarcation can be drawn 

 between groups B and C. By alteration and subsequent elimination 

 of the felspar, and conversion of the augite to hornblende and chlorite, 

 gabbros and dolerites may pass easily into rocks indistinguishable 

 from some of those of C. Since the change from augite to hornblende 

 by the action of dynamic agencies is now recognized to be a common 

 one, the intermediate stage of diorite and amphibolite may also have 

 occurred, so that some of the altered rocks may show resemblances 

 more to the amphibolites than to the original gabbros or dolerites. 

 The bases of distinction that have been adopted between the two 

 groups are more or less arbitrary, viz., the presence or absence of the 

 remains of felspars, and a recognizable structure. 



4. Description of the Rocks. 



A. The Quartz-Keratophyee. 



1 . General. 



Of the field relations of this rock little can be said with certainty. 

 ITowhere does it outcrop at the surface. Though specimens have 

 been collected from various dumps, in most cases the shafts associated 

 with these dumps are now inaccessible. In the few instances in 

 which the rock is found in the mines, it occurs in association with 

 talc-chlorite rocks, but owing to the great amount of alteration 

 of various sorts its relations cannot be made out with any degree 

 of clearness. According to Mr. Feldtmann, however, there are a few 

 instances in Avhich it does occur in tongue-shaped and dyke-like 

 masses, as at the 120 ft. level, south shaft of G.M.L., 4406 E., 

 Hyman, and consequently is to be regarded on field occurrence more 

 as an inti'usive porphyrite than as an andesite. 



Characteristic of the rock-mass is its peculiar blotchy or jointed 

 structure. In hand - specimens from yellowish - brown to dark 

 brownish-grey the specimens are, for the most part, comparatively 

 fresh, of medium grain, and with occasional small phenocrysts of 

 felspar. In the darker varieties small green spots are frequently 

 observable, while in all varieties are minute brownish-red patches, 



^ BocTis of Cape Colville Peninsula, vol. i, pp. 135-7. 



