PROCEEDINGS OF SECTION C. 417 



Ail inner escarpment runs for many miles parallel with the outer, 

 and is but little inferior to the latter in height and impressiveness. In 

 descending order, there follow very characteristic purple slates, which, 

 in part, are in vertical position ; and then a series of oolitic, dolomitic, 

 and siliceous limestones, interbedded with flags and slates, representing 

 several thousands of feet in thickness. A lower set of flags, slates, and 

 limestones complete the section to Blinman. On the western side of 

 Blinman the beds (allowing for a certain amount of curvature in the 

 strike) have a uniform dip to the west. On the eastern side of Blinman 

 the beds are repeated with a uniform dip to the east, until the Erin- 

 gundah Creek is reached, 10 miles from Blinman, when the Archceo- 

 ■cyathincB limestones again appear in the section, and the folding becomes 

 synclinal of a roughly periclinal type. 



Near the Eringundah Creek the Archceocyathince limestone bifur- 

 cates; one limb runs north-easterly to Wirrialpa Old Station and the 

 Mount Lyall Kange ; the other trends south-easterly to the Balcoracana 

 Creek. This periclinal basin brings into view a set of beds which are 

 superior in position to the ArchceocyathincB horizon. They consist mainly 

 of a series of red, softish, sandy flagstones, with purple slates, and a few 

 small limestones. One of the latter is highly fossiliferous in a narrow 

 horizon. Shells of Oholella, Orthis, Hyolithes, Girvamlla nodules, 

 and other remains are sometimes matted together in a confused mass. 

 ArchcBOcyathince are also sparingly represented in this bed, and there 

 is an horizon of sandy limestone which carries undoubted evidences 

 of annelid burrows. This fossiliferous horizon can be traced for miles 

 in the Wirrialpa and Balcoracana country. A marked topographical 

 feature of this upper series of beds is the presence of thin-bedded 

 quartzites or flags, which form a group of jagged peaks, five miles from 

 Wirrialpa Station, and are known as the Grindstone Range, or the 

 ■" Little Bunkers." These hills die away to the plains on the east, and 

 are the highest horizon of the Cambrian rocks known to me. 



There are two points of special interest which should be mentioned 

 in this generalised review of the geology of the Flinders Ranges. One 

 of these has reference to the conditions of deposition. It is usually 

 admitted that red rocks indicate subaerial deposits, either seolian, or 

 shallow water in combination with the latter. The upper (that is the 

 Flinders series) is characteristically of a red color, especially in the 

 higher members ; the beds largely consist of loosely cemented, reddish 

 sand grains, and are frequently false-bedded, of a kind which suggests 

 wind action. Further, the limestones, other than the dolomites, are 

 usually under three kinds of structure : (a) finely oolitic, (6) coarsely 

 concretionery, or (c) finely laminated. Observations made in the south- 

 ■east of this State have led to the discovery of an oolitic rock now under 

 formation. In this case concretionery granules of carbonate of lime 

 are forming on calcareous flats where the sand is saturated with water 

 but still exposed to the air. Where this occurs the surface appears 

 dry, but on scraping away the oolitic sand the deposit is found in a 

 wet condition. Oolitic concretions, I assume, are most likely to form 

 when evaporation of shallow waters containing calcium carbonate in 

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