﻿Vol. 64.] CAMBEIAN AGE IS SOUTH AUSTRALIA. 255 



quartzites) forms prominent ridges. The more yielding banded 

 slates of the Tapley's-Hill Series, which overlie the till, have 

 weathered into the low-lying ground between the ridges. The 

 highest member in the section is the equivalent of the Brighton 

 Limestone, of the type-district, and is strongly developed in a 

 synclinal trough between Pekina and Orroroo. The Mount-Grainger 

 Gold-Mine is situated in the till-bed, the gold occurring with 

 quartz-veins, and also clinging to the external surfaces of the 

 boulders which are fed to the stampers for the recovery of the 

 gold. 



Pig. 12 (p. 257) is a geological section taken at right angles to 

 that shown in fig. 11, following a south-and-north direction, from 

 the Yunta Eanges in the south to Oopina in the north, covering a 

 distance of 30 miles. This line of section crosses the Petersburg & 

 ]S^ew-South- Wales Border Hallway at Yunta Hailway-station. The 

 section is nominally along the line of strike (which is indicated in 

 the section at Teetulpa, and the Bushy-Peak Range) ; but the beds 

 are in places strongly influenced by periclinal folding, which throws 

 the strike into curves and creates a dip along the prevailing line 

 of strike. The tiU appears in four distinct outcrops, and the 

 associated beds are similar to those which occur in the same relation 

 in fig. 11. 



YI, General Considerations. 

 (a) The Ice- Agent. 



The nature of the ice-agent which operated in laying down the 

 vast accumulations of morainic material (represented by the Cam- 

 brian glacial beds) is of great interest, as bearing on the physical 

 geography of these latitudes in early Cambrian times. The weight 

 of evidence seems to be against the hypothesis of land-ice, of any 

 great extent, existing within the area concerned. In no instance 

 has the morainic material been seen resting unconformably upon a 

 rock-surface of an earlier period. There is consequently no glaciated 

 ' floor,' which might be expected to occur in the case of land-ice of 

 considerable extent. 



Again, while usually there is a strongly-marked lithological dis- 

 cordance at the junction of the till and the immediately-underlying 

 bed, there is presumptive evidence that the morainic matter was 

 laid down in an area of continuous sedimentation. The great 

 Cambrian, geosyncline was at that time a dominant factor in crust- 

 movements, and would ensure an increasing marine area with a strati- 

 graphical sequence of deposits ; while the nature of the sedimentation 

 Avould be profoundly influenced by the encroachments of the ice- 

 borne material over the area. The suggestion made by Mr. H. P. 

 Woodward, in 1884,^ that this ' boulder- clay ' had its origin from 



^ ' Eeport on the Mines, Hills, &c. of the Eange to the East of Farina & 

 Leigh's-Creek Railway-Station ' Parliamentary Paper No. 40 (South Australia) 

 Adelaide, 1884, p. 3. 



Q. J. G. S. No. 254. s 



