Western Australia. 149 



In No. 11106, square, columnar, and other shapes of a turbid, 

 indistinctly twinned felspar, together with irregular patches of 

 calcite, appear in a ground-mass that consists of small square and 

 lath-shaped felspars, minute granules apparently of quartz, numerous 

 round grains of pyrites, and small scales of green chlorite. The 

 felspar, both of the phenocrysts and of the ground-mass, is more or 

 less kaolinized, so that determination of the species is diflScult. It is 

 highly pT-obable, however, that the rock is another variety of the 

 porphj'rite with felspar phenocrj'sts. 



10433 closely resembles 12331a and 12368. There are large 

 kaolinized phenocrysts of twinned albite in various forms in a ground- 

 mass of small felspar squares and laths, without any 'flow' structure, 

 and small interstitial plates of quartz. There are also large green 

 chloritic aggregates without definite shape enclosing talcoso fibres, 

 and usually hrown from iron oxide. These, no doubt, represent the 

 hornblende phenocrysts noticeable in some other sections. One or 

 two large plates of clear quartz are visible in places, and there are 

 occasional patches of brown-stained carbonate. 



12321 differs from the above only in having a larger development 

 of granular calcite and a tendency towards felted structure in the 

 laths of the ground-mass. A considerable amount of sericitic mica 

 also is distributed over the slide. 



In 12232 large deep- green chloritized hornblende columns and 

 prisms make their appeai'ance, often stained, however, by iron oxide. 

 They are disposed in a fine-grained ground-mass which consists of 

 more or less twinned felspar laths, and which closely resembles the 

 ground-mass of 12376. Felspar phenocrysts are not observable in 

 this slide. 



2937 and 10434. These are blackish, rocks with white, 

 somewhat lenticular spots of a white carbonate, which, as it gives 

 an effervescence with cold dilute H CI, though a feeble one, is at 

 least in part of calcite. In section green chloritic patches and 

 granular carbonate in rounded and columnar forms, as well as in small 

 grains, stand out of a ground-mass of minute lath-shaped and small 

 short columnar crystals of a twinned and turbid felspar. The 

 carbonate areas appear in places mixed with chlorite and quartz, 

 some, mainly chlorite, have almost exactly the form of cross- 

 sections and elongated forms of hornblende crystals (see especially 

 2937). It is possible, also, that some of the forms, though they 

 show no remains of twinning, represent original felspar phenocrysts. 

 Numerous small black grains of magnetite are scattered through 

 the mass. 



The rocks are difficult to place, but the character of the phenocrysts 

 and the nature of the ground-mass have led to tlieir being classed as 

 hornblende porphyrites. A slight tendency to the drawing out of the 

 white spots in a parallel direction is observable in the hand-specimen, 

 a fact presupposing some shearing action on the rock-mass. 



TiUl is a hard reddish rock with a few dark-green specks. In 

 section there are numerous stjuare and columnar phenocrysts more 

 or less decomposed with the production of kaolin and sericite. These 

 stand out of a ground-mass consisting of a few felspar forms, granular 



