416 PROCEEDINGS OF SECTION C. 



beds spread over a great extent of country in broad anticlinal and 

 synclinal foldings. In these northern districts there is not that definite 

 thrust from east to west which is so evident in the Mount Lofty Ranges, 

 and the contractions operating north and south (on the strike), ap- 

 pear to have almost equalled that produced in an east and west direc- 

 tion. The effect has been to produce periclinal folding, taking the form 

 of vast domes and basins, the latter producing the remarkable saucer- 

 shaped areas to which the name of " Pounds " has been given, as in 

 the case of the Wilpena Pound, the lUinawortina Pound, and others. 

 Where these features are imperfectly developed the strike follows 

 curves rather than straight lines, and is frequently helicoidal. This 

 curvature of the strike has produced in many places differential move- 

 ment in the mass, with the attendant features of blatter and horizontal 

 slickensides ; and not unfrequently an exceedingly complex system 

 of faulting and disturbance. 



A good illustration of the dome-structure, as well as presenting 

 one of the most complete sections of the upper beds of the Cambrian 

 series with which I am acquainted, occurs near Blinman. One line 

 of section across this vast dome may be taken from the Parachilna 

 Plains, near Lake Torrens, on the west, to the Grindstone Range, on 

 the eastern side of the Flinders Range overlooking the Lake Frome 

 Plains, on the east. The mining township of Blinman, which is about 

 2,000ft. above sea-level, forms the centre of elevation in the dome 

 structure, with the beds dipping away from this centre in all directions. 

 The broken edges of these beds standing out prominently as mural 

 cliffs, present striking features in the landscape. Geographically, the 

 section (a) represents an east and west line of 40 miles ; geologically 

 (making allowances for curvatures and other irregularities of strike), 

 it is supposed to represent about 20 miles across the strike, and includes, 

 approximately, the full diameter of the dome. The symmetry of the 

 dome is broken by an adjoining basin which is developed on the south- 

 east of Erungundah Creek. 



The great western escarpment, which makes d striking feature from 

 the railway line, rises abruptly from the plains to about 1,000ft. in 

 height, and forms an impassable rock face for many miles both on its 

 eastern and western sides. The angle of dip is high, and the wall of 

 rock on its western face probably represents a fault-scarp connected 

 with the great meridional fault indicated by the central valley of Gulf 

 St. Vincent, Gulf Spencer, and Lake Torrens. The rock consists, in the 

 main, of a very close-grained, siliceous quartzite, and is overlain by a 

 thick series of limestones, largely oolitic or dolomitic in the lower 

 members, and an ArchcBOcyaihincB coral reef in the upper portions. 

 These are amongst the highest beds of the Cambrian series exposed 

 on the western side. On the eastern side of the ranges we have a set 

 of beds, superior to the ArchceocyaihincB limestone, including Obolella 

 and Girvandla limestones, which are not seen on the western side. 



(o) This refers to a sketch-section which was exliibited at the meeting in a diagram, 

 showing the dome structure and succession of beds across the Flinders Ranges 

 in the direction mentioned. 



