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Central Australian plateau. Quartzite-conglomerate fre- 

 quently forms the lowest bed of the series, followed by 

 quartzites, sandstones, dolomitic limestones, micaceous slates, 

 shales, etc. The post-Ordovician, Ordovician, and the Cam- 

 brian, together, form the flanking ranges on the south to the 

 central plateau. The author has always held that these 

 "inner" beds are Cambrian. Mr. Brown was of like opinion. 

 Messrs. Tate and Watt, on the other hand, failed to separate 

 them from, and included them in, their Ordovician group. 

 They eliminated Cambrian strata altogether from the region, 

 "Oodnadatta to MacDonnell Ranges," and claimed that the 

 Ordovician succeeded the crystalline pre-Cambrians uncon- 

 formably. 



The South MacDonnell forms one of the most conspicuous 

 ranges in Central Australia. Looking north from the 

 Hermannsburg Mission Station it presents a bold and striking 

 appearance — bare masses of rock, rising in tiers to the north, 

 culminating in dome-shaped hills and bluffs. Viewed from 

 east or west a succession of sharp, high peaks and serrated 

 ridges are seen. To the westward the ranges come to an end 

 a few miles west of Mount Tate. They run eastward, also, in 

 similar form as far as Alice Springs, a total of 150 miles, 

 with an average breadth of eight to ten miles. The rocks dip 

 south, between 15° and 90°, but the average is a steep dip 

 throughout that distance. The higher ridges are quartzite 

 and quartzose sandstone. The limestone and shaly beds, 

 interstratified with the quartzites, have weathered away, and 

 now form valleys through which we may travel, with high 

 walls of rock on either side, almost the entire length of the 

 ranges. The age of the beds making up this mountain mass 

 is trifold, viz., on the south, post-Ordovician; the central 

 portion, Ordovician; and the northern, Cambrian. 



From Alice Springs (Heavitree Gap), eastward, for 20 

 or 25 miles, the post-Ordovician and Ordovician strata are 

 apparently absent — or, more probably, covered by alluvium — 

 but beyond that distance they appear again and run on in un- 

 diminished strength for many miles. The Cambrian strata, 

 on the other hand, suffer no break, being continuous through- 

 out. East of Alice Springs the ranges extend for 150 miles. 

 The South MacDonnell Ranges are therefore not less than 

 300 miles long. The high quartzite ridge at Heavitree Gap 

 runs east for 20 miles to Mount Undoolya; it then takes on 

 a north-easterly course to and beyond Mount Benstead. It 

 forms the most conspicuous and at the same time the highest 

 part of the ranges, standing up 800 and 1,000 ft. above the 

 plain — a bare wall of rock well above everything else. The 

 dip is south, varying from 45° to 70°, and even steeper, in 



