293 



river system, as, for example, at Blackwood, Happy Valley, Morphett Vale, etc. 

 In this fluviatile valley, Blackwood would represent the eastern side of the ancient 

 river valley, Morphett Vale about the centre, and the coastline the western banks 

 of what is now a "dead" river. 



On the landward side of Curlew Point there occurs one of the most ex- 

 tensive washouts to be found along the coast. A wide gully has been excavated 

 by the rain, bounded by bare and vertical walls, 150 feet in height, and extends 

 inland for about a quarter of a mile, and then, at its head, bifurcates in north 

 and south branches (Howchin, W., 1918a, p. 70, fig. 54). It forms a remarkable 

 exposure of the Pleistocene, or later, fluviatile beds. Its recent origin is indicated 

 by the slight impression that the outflowing water has made on the nearly vertical 

 sea-clifT, giving the features of a "hanging" valley. 



The following is a Geological Section of the beds as exposed a little north of 

 Rocky Point : — 



Geological Age. Estimated Thickness. 



Recent — Nodular travertine .... . . . . . . 15 feet 



Sands and clays . . . . . . . . . . 20 feet 



Pleistocene — Mottled sandy clays with layers of hard white 

 sandstone and water-worn pebbles, -the harder beds show- 

 ing vertical jointing . . . . . . . . . . . . 30 feet 



Lower Pliocene — Hard, gritty, siliceous, and calcareous sand- 

 stone, containing casts and impressions of fossils, coated 

 on top with a nodular travertine . . . , . . . . 5 feet 



Cambrian — Rotten, purple-coloured slates . . . . . . 50 feet 



(Underlain by very siliceous quartzites that outcrop on the beach) 



SUB-SECTION C. 

 ROCKY POINT TO THE MOUTH OF THE ONKAPARINGA RIVER 



(3 MILES). 



Cambrian Rocks in Section C. 



The Cambrian rocks make only a small exposure in the cliffs from Rocky 

 Point to the outlet of the Onkaparinga River. The south-westerly strike of the 

 beds having taken the strong outcrops of quartzite to seaward, the soft purple 

 slates, overlying the latter, offer only a feeble resistance to the action of sea and 

 rain, and, in consequence, the Cambrian beds disappear from the cliff sections 

 within a short distance to the southward of Rocky Point, their place being taken 

 by newer beds. 



From Rocky Point to the outlet of Morphett Vale Creek (a distance of 

 about three-quarters of a mile) a remarkable combination of geological features 

 present themselves (see fig. 1). The cliff's being composed of comparatively 



Fig. 1. 



Section of Clififs on the Northern side of Morphett Vale Creek. 



S, Sand dunes. T, Travertine. R, Recent Clays. L, Pleistocene Clays and 



Sandstones. (See pi. xxiii., fig. 2, which gives a section of these beds writh hard 



bed on top.) P, Lower Pliocene Fossiliferous Bed. W, White Sand, partly 



argillaceous. C, Cambrian Rotten Slates. 



