PRESIDENTIAL ADDRESS. 21 



N.N.E. (true), dipping at 40° to E. 21° S. (true). Mount 

 Woodroffe, 5,200 feet nigh, in these ranges is perhaps the 

 highest peak in South Australia. Beyond the western end 

 of the Musgraves rise the Mann and Tomkinson Ranges. 

 The Mann Ranges, also formed mostly of Pre-Oambrian 

 rocks, exhibit planes of foliation and schistosity trending 

 from between N.E. and S.W., to W. by N. and E. by S. The 

 folding as shewn by Basedow (op. cit., p. 62 and PL xix) is 

 intense but not very asymmetrical. As far as can be judged 

 from his figure there is a slight tendency for the folds to be 

 forced over towards the north. 



The Tomkinson Ranges, formed of Pre-Oambrian gneisses 

 and schists, also have large intrusive dykes of olivine- 

 gabbro and norite. The gabbro intrusions trend about E. 

 and W. Diorite dykes follow the same trend. The planes 

 of foliation of the gneisses trend north-easterly (Basedow, 

 op. cit., p. 75). In Ayers Range the gneissic folds have a 

 general trend a little S. of W. and E. of N. 



At Mount Conner there is a great unconformity between 

 the Ordovician quartzites and the Pre-Oambrian crystalline 

 group. The strike of the quartzite varies from W. up to 

 W. 30° N. (magnetic). Mounts Kingston, Olga, and Ayers 

 Rock are formed respectively of quartzite, conglomerate 

 and metamorphic grit, considered by Tate and Watt to lie 

 at the base of the Ordovician Series. 1 The Levi Ranges to 

 the south of the MacDonnell Ranges are also formed of 

 Ordovician rocks and folded according to the same authors 

 on approximately E. and W. axes. The folds appear to be 

 nearly symmetrical. 



In the MacDonnell Ranges the same authors show that 

 the Pre-Oambrian gneisses, schists, and quartzites of that 

 region are very strongly folded, and that the trend in the 

 central and eastern part of the MacDonnells is nearly E. 



1 Rep. Horn Exp. Centr. Austr., General Geology , p. 59. 



