31 



ties o£ tlie gorge. The plateau of tlie Older Tertiary rocks in 

 whicli the gorge of the lower section of the river has been 

 formed ends in a comparatively lofty escarpment at Overland 

 €orner, which Captain Sturt estimated at 200 to 300 feet. 

 This was an over-estimate for the cliffs, though it might be 

 correct for the plateau. The cliffs are, however, higher there 

 than anywhere else on the river. What is the line of the es- 

 carpment back from the river I do not know, but abutting 

 against that escarpment are beds of Newer Tertiary age, 

 formed chiefly of loose material, constituting a plateau the 

 mean elevation of which is below that of the escarpment at 

 Overland Corner. 



The materials of the minor plateau are of fresh-water origin 

 — at any rate, no palaeontological evidences have been adduced 

 for or against — whilst the extreme angularity of the sand con- 

 stituents and their false bedded arrangement demonstrate 

 rapid accumulation such as takes place where torrential 

 streams debouch into lake basins. We may apply here Sir A. 

 C. Eamsay's opinion to the determination of the physical con- 

 ditions under which the formation was deposited. He has 

 stated* that the red colour which stains the Iveuper Sandstone 

 and Marl is due to the presence of peroxide of iron, which he 

 believes to have been precipitated from carbonate, and which 

 could only have taken place in inland isolated waters ; an 

 opinion that is confirmed by other facts which tend to prove 

 that the rocks in question were formed in a lake or lakes. 

 This belief he afterwardsf extended to formations of older 

 date. 



The sharp sands, which form a considerable part of the 

 material of the cliffs of the upper, section of the river, not only 

 vary in size, but also in colour, some portions being quite 

 colourless, whilst others are deeply stained with red, and in 

 several instances the oxide of iron has compacted the material 

 into a firm grit- stone. In all cases the red colour of the sands 

 or grits is superficial, as by treatment with hj^drochloric acid 

 it is totally discharged. Here, then, we have non-fossiliferous 

 sands, highly stained with hydrated oxide of iron, whilst the 

 other physical conditions under which they were accumulated 

 all tend to confirm the view that they were formed in inland 

 waters, and not in an open sea. However, this much is certain, 

 that since the elevation of the Older Tertiary sea-bed to form 

 the Murray Plain, some portions beyond Overland Corner have 

 been denuded, and that a considerable depth and vast quantity 

 of sands and loam have been deposited against the escarpment 



* Quart. Journ. Geol. Soc, vol. xxviii., pp. 189, 1871. 

 t Op. cit., p. 241. 



