ACADEMY 0F8CI-NCE8] AUSTRALASIA. 37 



The ultrabasic rocks of the Mount Wellington area have also been described by Teale ('20) . 

 Here there occurs an elongated mass of serpentine running for a distance of over 3 miles in a 

 northwesterly direction with a width varying from two chains to a quarter of a mile. It lies 

 between black jasperoid slate, and black slate with bluish calcareous bands in which Upper 

 Cambrian fossils occur (Chapman '11). A serpentinous conglomerate is associated with the 

 slate, and the serpentine is therefore regarded as older than the slate. It contains besides 

 chromite a considerable amount of corundum. 



In the pre-Cambrian complex of Broken Hill, New South Wales, Andrews ('22) and his col- 

 leagues have found two series of basic igneous rocks. The older consists of laccolitic or sill-like 

 masses for the most part, but also form dikes in the sedimentary schists and augen-gneisses. 

 They comprise more or less altered peridototes, pyroxenites, gabbros, and norites, and are inti- 

 mately associated with dike-like masses of an aplitic rock rich in barium, and gamet-quartz- 

 magnetite rocks. A noteworthy feature is the frequent association of fine and coarse grained 

 types of gabbro, probably as the result of successive injections of magma into the plane of the 

 sill. The newer series consists merely of dikes of uralitic dolorite, possibly of post-Cambrian age. 



In southeastern New South Wales a band of peridotitic and pyroxenic serpentine extends 

 from near Tumut to beyond Gundagai, a distance of 40 miles. It has been traced by Carne 

 ('92, '95), who has shown it to follow approximately parallel to the nearly meridional line of 

 strike of the probably Ordovician rocks which it invades, while smaller parallel bands occur 

 associated with it. No definite evidence of its age is available, nor is there definite information 

 of the time and conditions of intrusion of the norite of Kiandra (Andrews '01) or the serpentine 

 of Berthong (Jaquet '96) . Considerable folding seems to have occurred between the times of 

 deposition of the Ordovician and Silurian rocks, for the two series are generally unconformable, 

 but no plu tonic intrusions have yet been shown to have formed in this interval. Sussmilch ('14) 

 and Andrews ('16) conclude that during the Devonian period a movement of folding strongly 

 affected the eastern portions of southern New South Wales, the strikes of the two epochs of 

 folding being parallel to each other and to the Gundagai serpentine-belt. 



There appears less uncertainty in regard to the great serpentine-belt of northeastern New 

 South Wales which has been studied in detail by the writer. (See Benson '13, '15, '17, '18.) It 

 seems that no folding occurred from Middle Devonian until Middle Carboniferous times, when 

 the orogenic movements commenced. The sequence of events is as follows : The belt of country 

 extending northward and to the north-northwest of Newcastle was a geosynclinal area during 

 Devonian and early Carboniferous times. In this was deposited a great thickness of radiolarian 

 sediments, interstratified with three bands of Middle Devonian coral-limestone. Submarine 

 eruptions took place producing an immense amount of tuff, breccia, and agglomerate, with 

 accompanying formation of probably intrusive spilites, and vesicular pillow-lavas and dolerites 

 (diabase), generally albitic, 1 with locally large amounts of very albitic keratophyre. This series 

 of rocks in regard to their age, the tectonic conditions of their origin, their sedimentary 

 associations, and their mineralogical characters, are most closely allied to the spilitic suite of 

 rocks of Devonshire, Germany, and probably also to those of the Urals. (Compare, e. g., 

 pp. 12, 16, 19, 20, above.) But the comparison does not cease here. In Upper Devonian 

 times deposition of radiolarian mudstone and tuffs continued with rare intrusions of dolerite 

 (Benson '17). In early Carboniferous times (perhaps after an erosion-interval and con- 

 sequent disconf ormity) [ the deposition of mudstone (but not radiolarian) continued with 

 formation of interstratified crinoidal limestone in small amount; later keratophyric tuffs 

 appeared more abundantly, followed by a great series of conglomerates and tillites 

 (the development of which seem to indicate the commencement of crust-folding), with 

 tuffaceous sandstones with plant remains of lower to middle Carboniferous age (Walkom '19) 

 invaded by an extensive series of igneous rocks rising through longitudinal and transverse 

 fissures. These intrusions appear to have been closely connected with the outpouring of the 



i The examination of a sill of albite-dolerite 1,300 feet thick showed that it was uniformly sodic, a contrast to the concentration of albitc in tho 

 upper portion that might have been expected on the' hypothesis of the upward concentration of Sofia by resurgent water. (See Daly '14, 

 Benson '15.) 



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