30 HORN EXPEDITION — GENERAL GEOLOGY. 



to the Cainhriaii]. (-) Tlie beds of the tableland of the Great Austral Plain in 

 the vicinity of Dalhousie Springs are described as consisting of a great argillaceous 

 series crowned by porcelainised sandstone ; they are considered " to be Mesozoic 

 (and probably Cretaceous)." The porcelainisation of some of these strata is 

 considered to be due to submergence in silicated waters which are wholly 

 evaporated (p. 51); and it is noted that "the obsidian bombs are most numerous 

 among the portions of the plain whose surface is strewn with chalcedony and 

 ironstone nodules " (p. 53). The foundation rocks of " the Terraces " consist of 

 fissile .sandstones, argillaceous and siliceous limestones, as in Mount Charlotte 

 ridge, and appear in gentle undulations, which become more and more sharply 

 curved on approaching the McDonnell Range (pp. 46, 51). The central plateau 

 consists of impure limestone and an underlying red quartzite, which forms the 

 south edge of the central plateau and rests on gneiss and granite intersected by 

 diorites — the whole, from Lake Eyre to the Burt Plain, representing a conformable 

 series (p. 47), though a doubt is expressed with regard to the rocks of the 

 McDonnell Range, which, on the ground of their degree of metamorphism, may 

 perhaps be considered Archaean (p. 51). [(3) Nevertheless, the schistose rocks at 

 Polly Springs are compared with the primary rocks of Denison Range]. (4) De- 

 scribes gravels containing large boulders of granite and schist on the north Hank 

 of Cunningham Cap, and suggests their derivation from " a bar of primary rocks," 

 of which those at Polly Springs may be a remnant (p. 44). 



IX. — Brown, Henry Y. L., " Rejjort on a Journey from Adelaide to Hale 

 Rivei," Pari. Paper, S.A., No. 24, 1889, with M;ip and Sketch Section. "From 

 Mount Dutton northward to the vicinity of Mount Burrell the whole country is 

 occupied by tiie Cretaceous and Tertiary formation." Extinct mound-springs are 

 stated to occur at Dalhousie Head Station. In the vicinity of Mount Burrell, 

 commencing three miles south from it, are crystalline limestones with flinty veins, 

 quartzite slaty sandstone and cleaved slates ; these are considered Primary (pro- 

 Ijably Silurian). Overlying these, first seen at and northward of Oorauiinna Well, 

 are brown and white sandstones, which are classed by the author as Devonian (?) or 

 Silurian. The red quartzites and overlying beds which form the southern barrier 

 of the McDonnell Ranges are included with the granitic and metamorphic rocks 

 which compose the main ranges under the head of Azoic. 



X. — Brown, Henry Y. L., " Report of (Jeological Examination of Country 

 in Neighbourhood of Alice Springs," Pari. Paper, S.A., No. 189, 1890. The 

 fundamental rocks of the McDonnell Ranges are various metamorphic rocks with 

 eruptive dykes of diorite, pegmatite and coarse granite. Resting unconformably 



