BY \V. X. BENSOX, W. S. DUX^ AXD W. R. BROWXE. 411 



Many of tbe more albitic types are eliaracterised by ortliopliyrie fabric. We 

 may take as an (Example 1408, from a dyke in Duri Creek, S.E. of Duri Peak, 

 cutting' through the Kuttung- grits and conglomerates. Phenocrysts of albite up 

 to 3 mm. long, sometimes aggi-egated in glomero-porpliyritic fashion, are set in a 

 matrix of stumpy prisms of albite averaging about .25 mm. long and at least 

 as acid as Aboo Anio in general composition. The spaces between these are filled 

 with quartz, which composes about 10 % of the rock. The felspar is much 

 kaoliuized and stained witli haematite, and disjiiays a narrow clear him round a 

 decomposed kernel. Tiny crystals of magnetite are fairly plentiful and little 

 apatite needles and biotite flakes are infrequent . 



Another rock (1499) resembles 1498 except for the presence of definite il- 

 menite much leucoxenised, and that the biotite is chloritized (PI. xxv., fig. 4) . 

 This rock occurs as a sill which passes into the dyke from which the pre\'ious 

 specimen was taken. Another specimen (1.530) from the same dyke diffei-s in 

 the lugher proportion of iron ore and in the smaller amount of biotite, which is 

 reiJresented by a little chlorite. 



A dyke which occurs in Portions 240 and 178 may be connected with the 

 Warragundi volcanic centre, and belongs to the orthopluTie type, differing from 

 the rocks just described only in having slightly coarser texture and having more 

 interstitial chlorite . 



A much more basic though allied type is 1528, from a dyke 24 yards wide, 

 half a mile north of Portion 1. This has a much higher proportion of iron ore 

 than the others, while ferro-magnesian minerals are represented by abundant 

 augite. The grain-size is coarser, too, the felspars averaging about .6 mm. long, 

 and the rock is non-porphyritic. Felspar (Abn.-, An-,) is slightly zoned, and ha.s 

 the usual clear rim round a decomposed kernel. The interspaces between the 

 felspars are filled chiefly with abundant jiale granular augite, iron ores and very 

 subordinate quartz. Augite and magnetite are also included in felspar. Tiny 

 apatite needles are fairly numerous, while chlorite is (juite common, often filling 

 cavities . 



In 1494 (dyke crossing Rocky Creek) and 1490 (dyke in the S.E. of Portion 

 11), the texture is finer than that of 1498, and there is rather more elongation of 

 the felspars of the base, although their general composition is still very acid, about 

 Aba.'-, An.-,. Ilmenite is fairly plentiful, and may appear among the phenocrysts. 

 The felspars are much replaced by carbonates, but the rocks were evidently de^■oid 

 of ferro-magnesian silicates. Vesicles in 1496 are filled with calcite, and partially 

 lined with little quartz prisms. 



These two rocks may very probably represent dykes radiating from Warra- 

 gundi. A dyke (1511) from the N.E. corner of Portion 70, Werrie, has much 

 in common with them, but has rather more iron ore and retains chloritic pseudo- 

 morphs after (?) hornblende. 



There are a number of very fine-grained rocks (1437, 1514, 1529) consisting 

 mostly of lath-shaped or acicular felspars, apparently oligoclase, and exhibiting a 

 more or less perfect trachytic habit. Orthodase is sometimes associated with the 

 other felspar, generally in subordinate amount, but its presence is not always 

 recognisable. In all of these there is practically no evidence of the former pre- 

 sence of ferro-magnesian constituents, though mag-netite is plentifully dusted 

 through the rock. Small phenocrysts of oligoclase are jiresent, and there is much 

 alteration to kaolin and carbonates. Cavities are filled with chalcedonic quartz. 



