BY W. K. DEXSOX, W. S. hVS , AXL W. K. BROWNE. 



421 



Patches of calfite are sporadically distributed and tiny vesicles are filled with 

 ualcite, or with chlorite, chalcedonie quartz and a hexagonal (?) zeolite. 



(c) Teschenitic Dolerite. An interesting rock, and the only one of its kind 

 so far discovered in the area, is that forming the sill or dyka about half a mile 

 S.E. of Currabubula Railway Station. It is megaseopically fine and even- 

 grained, with felspar apparently constituting a little less than half of the entire 

 rock. JVIieroscopically it is subophitic in fabric. The augite is titaniferous, 

 purplish-brown and pleochroic, and occurs in two ways: (1) as largish subidio- 

 morphic to allotriomorphie individuals, often ophitic towards felspar, and (2) as 

 nests or clusters of small stout well-foi-med prisms. Felspar is in elongated laths 

 up to .8 mm. in length, slightly decomposed, and is labradorite bordering on 

 bytownite. 01i\-ine, usually enclosed in augite. is fairly abundant, sometimes as 

 large regular gTains, but generally in small roimded prisms, much cracked and 

 altering peripherally to a brown-gi-een serpentine . Fresh subidiomorphic ilmenite 

 is plentiful, often surrounded by tiny flakes of biotite, and apatite is very abund- 

 ant. There is a mesostasis composed of analcite which makes up at lea.st 25% 

 of the rock and often completely encloses tiny crystals of most of the other 

 minerals, particularly augite and apatite. Indeed the bulk of the apatite is found 

 in the analeitic mesostasis, which recalls the fact recorded by Dr.. Elsdeu in regard 

 to certain of the quartz dolerites of St. David's Head (53) that the interstitial 

 quartz contains over 70 % of the apatite present in the rock, indicating a very 

 high solubility for this mineral under the conditions obtaining in the magma. 

 The analcite is always interstitial, never forming definite crystals. It is in some 

 places quite clear, but elsewhere is quite turbid, and flecked with highly bire- 

 fringent alteration products. Occasionally its place may be taken l)y calcite. 



It is now generally agreed that the analcite of teschenitic rocks is often to be 

 regarded as belonging to the period of primai-y rock crystallization, and to re- 

 present the consolidation of the last watery soda-rich magmatic fraction (54) (55). 

 In the present instance the analcite has all the appearance of a primary mineral 

 of late crystallization. It has attacked the felspars to a very slight extent, but the 

 augite inclusions present well-marked and unaltered boundaries, and there is no 

 development of a soda-rich border (55) . The serpentinization of the olivine may 

 possibly be, as Bailey has suggested, due to the action of residual magma or 

 "juvenile" waters (54a) . 



Gexeral Remarks. 



The foregoing investigation establishes the essential correspondence between 

 the rocks of the Warragundi complex and those of the intrusions at a distance 

 from that centre. Some points of difference have been noted, but the conclusion 

 of a close mutual relationship seems inevitable. 



If we consider the series as a whole, tuffs, flows and intrusions — and this 

 seems a reasonable tiling to do — a curious association of alkaline and calcic types 

 is revealed. On the one hand there are the typical calcic andesites and dolerites, 

 and on the other the soda rhyolites and keratoph^'Tic rocks, tlie albitic dolerites 

 and the tuffs, both sodic and potassic — an assemblage of distinctly alkaline facies. 

 The two groups are of equal importance in tlie series, and. as we have seen, are 

 linked by intermediate types, so that there can be no doubt of their derivation 

 from a common stock-magma, a conclusion with which th« field evidence is in com- 

 plete agTeement. What was the nature of the original magma we can only con- 

 .-'ecture. In dealing with the rocks, of the Seaham-Paterson-Clareucetown area 



