64 HORN EXPRDITION — GENERAL GEOLOGY. 



Johnston's Ranf;;e. — (1), Desert sandstone, 6 to 8 feet; (2), soft white 

 felspathic sandstone, 25 feet ; (3), more indurated red sandstone, 25 feet ; (4), 

 soft grey argillaceous sandstone, 70 feet. The dip of the beds is about 6° nearly 

 due south. Giles describes the north escarpment of this line of elevation 

 as exhibiting successive planes of water-erosion, but his " water lines " are 

 simply the effect of alternating bands of variously-coloured rocks, seemingly 

 horizontally bedded, as viewed on the line of strike (east and west, which is also 

 the bearing of the escarpment). 



The main mass of the Upper Cretaceous reaches as far north as the latitude of 

 Engoordina, as at Mount Squires, near there, and Johnston's Range, further west. 

 North of this latitude much of the country is buried beneath sandhills and river 

 drift. Bluffs along the margin of the River Hugh, below Alice Well, and to its 

 junction with the Finke, are composed of unaltered sandstone, and they occasion- 

 ally occur northward to about seven miles south of Mount Burrell. Of these 

 outliers Chambers' Pillar is the most conspicuous. In an amphitheatre-like 

 depression in the Ordovician limestones, through which flows Alice Creek, there 

 occurs a micaceous shale as brought to light by a well sinking, which is probably 

 of Upper Cretaceous age, and if so, then the most northerly occurrence in this part 

 of Australia. For the most part, the stratification of the Upper Cretaceous is 

 apparently horizontal, though slight undulations of far-reaching extension prevail 

 in the northern area occupied by these rocks. 



Relation to Artesian JFaters. — It has generally been held that the source of 

 supply of the Natural Artesian Wells on the west side of Lake Eyre was derived 

 from tropical rains in Queensland ab.sorbed by Cretaceous outci'ops, and that the 

 issue of the.se waters was along the line of junction of the Ci'ctaceous water-bearing 

 beds with the Palaeozoic rocks on the west mai'gin of Lake Eyre. But the now- 

 ascertained far-northerly extension of the Cretaceous rocks, and the replacement 

 of the prevailing argillaceous condition by sandy strata towai'ds the northern 

 boundary make it probable tliat the source is, after all, of local origin. Thus, the 

 Finke River from Henbury to Crown Point flows approximately along the junction 

 of the Cretaceous arenaceous beds and the impervious Ordovician limestones ; so 

 also do the Goyder and Lilla Creeks, particularly towards their sources. Moreover 

 the Cretaceous beds have in the main a slight southerly inclination. It is, 

 therefore, highly prol)able that they do absorb some of the flood -waters of those 

 river-channels, and conduct them to considerable depths in the depressed area 

 margining Lake Eyre ; whilst in no instance do the subterranean waters issue at 

 the surface at a level so high as that of their conjectural intake. The phenomenon 



