82 



of the Upper Cambrian Division that have been hitherto 

 recorded in South Australia. With the exception of a thin 

 bed of laminated and contorted limestone that occurs a little 

 higher in the series than the Archaeocyathinae horizon, these 

 top beds are not much disturbed. They consist, mostly, of 

 softish and highly-coloured sandstones and shales with one 

 highly fossiliferous horizon (the Oholella limestone), which is 

 of no great thickness. 



As to the physical conditions under which the beds were 

 laid down, the evidence seems to point to shallow water, if not 

 dry land conditions, at some horizons. Some of the limestones 

 have a nodular, or subglobular, kind of structure, which is 

 seen on the weathered surface, and when split by the hammer 

 break up into more or less rounded fragments, which have a 

 close likeness to the surface concretionary travertines that form 

 in calcareous soils under an arid climate. A specimen picked up 

 near the old Wirrealpa station showed what had been, in the 

 first instance, projecting cups of Archaeocyathinae, and then 

 were contemporaneously surrounded by concre-tionary limestone, 

 such as might have been formed following on the elevation of 

 a reef of these organisms above the level of the sea. The 

 very common occurrence of oolitic limestones, and oolitic sand- 

 stones in which the oolitic grains and rounded sand grains are 

 mixed up together (very much as they occur in present-day 

 deposits laid down in a shallow lake, near Robe, which is 

 alternately wet and dry) (see Howchin's "Greology of South 

 Australia," p. 176, figs. 152-154). Still further, the red and 

 friable sandstones, much cross-bedded, near the top of the 

 series have features that favour the idea of a terrestrial origin. 



DESCRIPTION OF PLATE IV. 



Fig, 1. Geological sketch-section of outcrops from the mouth 

 of the Parachilna Gorge to the vicinity of Blinman. 



Fig. 2. Geological sketch-section from Blinman to the 

 northern side of the Erengunda Creek. 



Fig. 3. Geological sketch-section from The Bunkers to the 

 Eastern Plains. 



Note. — The Geological Sections, as described above, are made 

 as detailed as the nature of the outcrops permitted. The rapid 

 changes, in succession, of quartzites, shales, and limestones, within 

 short distances, render it impossible to note such occurrences, in 

 detail, within the limits of the scale adopted. The dip of the 

 beds, also, varies greatly, in places, within short distances. It 

 must therefore be taken for granted that the sections are, to a 

 large extent, generalized rather than exact. A further difficulty 

 jwose from the quaquaversal curves in the dip, so that in some 

 parts of the section the line follows a true direction of dip, while, 

 in others, it approximates to the line of strike, in which case 

 important beds, situated on one, or other, of the sides of the 

 section, and running parallel with it, could not be shown in section. 



