﻿Vol. 64.] CAMBKIAN AGE IN SOUTH AUSTRALIA. 241 



of the pre-Cambrian rocks of the country, while others cannot be 

 identified as such. At the time when the glacial deposits were laid 

 down, the pre-Cambrian floor, on the east side of the meridian of 

 Gulf St. Vincent, was covered by several thousand feet of Cambrian 

 ' sediments. The erratics of pre-Cambrian origin would probably, 

 therefore, have travelled -considerable distances before coming to 

 rest on the morainic banks forming in the Cambrian Sea. 



(c) Glaciatioiir 



Although the general features of the beds supplied a strong 

 prima-facie probability that they represented an ancient till, their 

 glacial origin was not affirmed until the discovery of ice-scratched 

 boulders placed the question beyond doubt. This culminating 

 evidence was obtained, in the first instance, at Petersburg (on the 

 Northern Railway from Adelaide) in 1901, and was subsequently 

 confirmed during a visit to the same place by Prof. T. W. E. David, 

 F.R.S., Mr. E. E. Pittman, the Government Geologist of New South 

 Wales, and myself. In association with those two experienced 

 geologists, fifteen glaciated stones were obtained during a search of! 

 two hours. i 



The erratics are frequently facetted, as well as striated, under 

 ice-action. The striae vary in depth and direction on the same 

 face, and are often as distinct and fresh-looking as those which 

 occur on the stones of the Pleistocene Boulder-Clay. Under strong 

 pressure and movement in their bed, some of the boulders exhibit 

 evidences of abrasion ; but this, as will be explained later, produces 

 features altogether distinct from glacial striation and cannot well 

 be confounded with it. 



That these ice-marked stones are a general characteristic of the 

 Cambrian till, is evident from their having been found in most 

 localities whenever opportunity permitted a search for them. 

 Some of the more interesting outcrops for their occurrence are the 

 Petersburg Ranges, the Depot Hill (near Black Rock, north of 

 Petersburg), Pekina Hill (near Orroroo), Mount-Cone Range (east 

 of Mount-Bryan Railway-station, where, in a single visit, thirteen 

 excellent examples were found), Appila-Creek Gorge (near Laura), 

 and the Daly and Stanley Mines (north-eastern parts of the 

 Elinders Ranges). A very powerfully-striated boulder was ob- 

 tained from the till, near the Burra ; and another was obtained 

 in situ, in the Willouran Ranges, near Hergott, at the northern- 

 most position in which the Cambrian glacial beds have been 

 determined. 



Up to the present, eighty very definitely-glaciated boulders have'^ 

 been secured from various localities in the Cambrian till, besides the 

 known occurrence of many other examples where the erratics were 

 too large for removal. Illustrations of a few of these ice-marked 

 stones are given in PI. XIX & figs. 2-5 (pp. 242-45). 



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