PROCEEDINGS OF SECTION C. -415 



iar as we are able to test it) goes to show that tHe old Cambrian moun- 

 tains of southern Australia, in their greater heights, have not been sub- 

 merged from the time when they were first raised above sea-level. From 

 the great waste they have suffered in the interval, it is reasonable to 

 conclude that the top beds, which would be particularly exposed to the 

 denuding agents, have entirely disappeared, so that we speak of the 

 top of the Cambrian series only in a relative sense. On the other hand, 

 the base of the system is well defined, and will be dealt with in the 

 sequel. 



The age of the beds is determined mainly on palseontological 

 grounds. With the exception of a few obscure remains of Radiolaria 

 in the Brighton beds, the fossiliferous horizons, so far as known, are 

 limited to two limestones very high in the series. These occur at 

 Ardrossan, Yorke Peninsula ; Sellick's Hill, 20 miles south of Adelaide ; 

 and at manv places in the Flinders Ranges. The most striking group 

 of fossils belong to the Archceocyathinre, which must have formed coral 

 reefs in the Cambrian seas of great geographical extent and from 100ft. 

 to 200ft. in thickness, in addition to which are the typically Cambrian 

 forms of Obolella, Stenotheca, Hyalites, Salterella, and some Cambrian 

 trilobites {Microdiscus, Olenellus, Ptychoparia, &c.), which unfortu- 

 nately, are mostly in a very fragmentary condition. This strongly 

 marked Cambrian fauna, occurring near the top of the series, fixes the 

 latest geological age that can be assigned to all the inferior beds in the 

 same series. As a matter of convenience, the beds above the Brighton 

 horizon, which include about two-thirds of the whole, may be called 

 Upper Cambrian (or Purple Slates series), whilst the beds below that 

 line may be designated Lower Cambrian. The former are best seen 

 in the Flinders Ranges and the latter in the Mount Lofty, Barossa, 

 and Petersburg Ranges. 



The physiographical features of the Flinders Ranges differ greatly 

 from those of the Mount Lofty. This arises partly from the different 

 climatic conditions of the respective areas, the southern districts having 

 a relatively moist climate and the northern districts an arid one. In 

 the latter case the stratification over great areas is as sharply defined 

 as when drawn on the blackboard : the hills have jagged crests and 

 peaks, and the limestones, instead of passing into solution, stand out 

 as prominent ridges. 



Another point of contrast arises from the variation which has 

 occurred in the folding force in the respective areas. In the Mount 

 Lofty and other southern districts the tectonic forces operated on a 

 grander scale, the axis of elevation reached a higher altitude, the crush 

 was correspondingly greater, and an anticlinorium of great intensity 

 was developed with numerous contortions, overfoldings, and thrust 

 planes. In the Flinders Ranges and in the country between Petersburg 

 and the New South Wales borders, whilst there has been much crush, 

 producing in places vertical and contorted stratification, the country 

 has not been contracted under pressure to the same extent as in the 

 case of the Mount Lofty Ranges. I am not aware of any place in the 

 Flinders Ranges where the base level is exposed, but the Cambrian 



