282 



On leaving the Hallett's Cove railway station, a walk of about a quarter 

 of a mile across the paddocks (passing some farm buildings in ruin on the way) 

 brings us to the top of the sea-cliffs. Near the edge of the cliffs a very siliceous 

 quartzite forms the outcrop, and although much broken and weather-flaked, still 

 shows some fine faces of glacial polish and striations. Resting on this glaciated 

 floor, on the landward side, is a bank of boulder clay, containing numerous 

 erratics. This marks the most northerly point where the evidences of Permo- 

 Carboniferous glaciation can be traced, the glacier path being here directed 

 seawards in a north-westerly direction. 



Immediately to the southward of this place, a small gully, running in an 

 east and west direction, finds its outlet on the beach. Standing on the right 

 bank of this gully, near its outlet, a rather remarkable section can be seen on 

 the opposite bank (Howchin, W., 1918a, fig. 307, p. 411). In the bed of the 

 stream and lower portions of the bank the Cambrian quartzites make a distinct 

 anticline, causing a small waterfall. Resting unconformably on this Cambrian 

 floor, which is well polished, is the glacial till ^^^ with its striated erratics, of Permo- 

 Carboniferous age. A further unconformity occurs by the fossiliferous Lower 

 Pliocene resting on the boulder clays ; while a still further unconformity arises 

 from the Pliocene beds being covered by clays, sands, and a thick bed of nodular 

 travertine of Recent age, making three stratigraphical unconformities in a sec- 

 tion of about 80 feet in thickness. These respective beds can be traced up the 

 small gully (referred to above) and- its tributaries for about a quarter of a 

 mile, where they run out against the Cambrian boundary. 



Crossing the small gully, at the waterfall, and climbing the bank of till on 

 the opposite side, at a distance of about 100 yards, the largest exposed face of 

 the glaciated floor in the locality is seen on a rather steep slope towards the 

 beach. The smoothed rock forms part of the Purple Slate Series, and has 

 taken a high polish with many broad groves and fine scratches which have a 

 north-westerly direction (Howchin, W., 1918a, fig. 308, p. 412). Some of the 

 latter give evidence of ricochetting by the stones forced along by the glacier 

 and repeatedly digging into the floor, in a series of jumps, with the deeper side 

 of the cut in the direction of the flow, like a jumping chisel, and thus establishing 

 by the clearest proofs the direction in which the glacier was travelling. Other, 

 but smaller polished faces, have become exposed by the denudation of the over- 

 lying beds near the extremity of Black Point, and are also seen wherever the 

 clay has been removed so as to expose the underlying glacial floor. 



The till, or boulder clay, resting on the Black Point shelf, is a relatively 

 thin deposit, averaging about 20 feet in thickness, and does not contain such 

 very large erratics as are scattered over the Cove and on the southern side of 

 the outlet of the Field River, but it has yielded some scores of strongly glaciated 

 stones from the till. The relationship which the glacial beds have to the fossili- 

 ferous Pliocene was, for some time, a question of discussion, but was set at 

 rest by an excavation, carried out under the auspices of the Australasian Asso- 

 ciation for the Advancement of Science [Report, 1895], when by a costean pit 

 it was proved that the boulder clay passes beneath the Pliocene beds. This 

 inferior position of the till to the Pliocene is also clearly shown in a section near 

 the head of the Cove. 



The glacial clay on the Black Point platform contains numerous nodules 

 of sandy crystals of barytes, the sand having been included in the barytes in the 

 process of crystallization. These nodules are usually from an inch to an inch 

 and a half in diameter. The crystals are grouped round an axis of growth 



(1) The term "till" is here used m preference to "tillite," as the Permo-Carboniferous 

 glacial beds of South Australia are invariably soft and friable, as in the case of modern glacial 

 deposits. 



