294 



soft rocks have retreated and are set far back from the beach, leaving a shelf of 

 broken and humpy ground, about a quarter of a mile in width, in which several 

 stratigraphical unconformities are visible. 



At about half-way between Rocky Point and the Morphett Vale Creek, and 

 ^midway between the beach and the high cliffs, there is an inlier of Cambrian 

 slates, bluish in colour, and so soft as to be easily mashed by the fingers, like 

 clay. These rotten slates are interbedded with occasional bands (up to 18 inches 

 in thickness) of a ferrugino-arenaceous character, making striking effects in a 

 contrast of colours. The dip of the beds is to the east at an average angle of 

 65°. There are no further exposures of Cambrian beds on the coast until a 

 short distance before reaching Blanche Point. 



(?) Pre-Pliocene Beds in Section C. 



Underlying the fossiliferous Pliocene beds, and resting unconformably on 

 the eroded edges of the Cambrian slates (as shown in text fig. 1) is a fresh- 

 water series of sands, argillaceous sands, gritty sands, and, occasionally, of fine 

 gravel, mostly of a whitish colour. The sand is unconsolidated, perfectly soft 

 and free to the feel and very uniform ; it carries no fossils, and whilst weathering 

 into what looks like laminar bedding, cannot be separated on the laminae, as it 

 has no cohesion, but is subdivided by layers of ironstone or ferruginously 

 cemented sand ; the bed exhibits false bedding in places, and has a slight north- 

 westerly dip. The plane of junction between this sand bed and the underlying 

 Cambrian slates is a ferruginous lateritic layer an inch or two in thickness. 

 This sand bed is seen to pass under the fossiliferous Pliocene bed on the northern 

 side, and increases to a thickness of about 30 feet on its southern. Following 

 which, the Pliocene sandstones have been removed by denudation, and the under- 

 lying soft sand bed has also been reduced by exposure and partly obscured by 

 more recent deposits. A similar bed of white sand underlies the fossiliferous 

 Pliocene at Hallett's Cove (see p. 288), but whether the bed, now under descrip- 

 tion, has a closer stratigraphical relationship to the overlying Pliocene, or to the 

 basal beds of the Miocene (seen further to the south), or corresponds to the 

 white sandstone that intervenes between the fossiliferous Pliocene and the glacial 

 till at Hallett's Cove, it is difficult to say. 



Lower Pliocene (Fossiliferous) Beds in Section C. 



Between the sea-stack (on the beach) and Rocky Point two indentations 

 have been made in the cliffs by rain erosion (see p. 286) by which excellent 

 sections of the beds can be seen. The fossiliferous Pliocene that disappears 

 at Hallett's Cove, from denudation, reappears in the two small coves just men- 

 tioned. When viewed from the beach the fossiliferous bed is easily distinguished 

 from the other geological formations and forms the sky-line ; but on reaching 

 its level it is found that there is still another cliff behind it. The hard sandstone 

 of the fossiliferous bed has protected the softer Cambrian beds beneath from 

 denudation, while itself, more resisting than the overlying beds, forms a shelf, 

 from the edge of which the softer beds of clay have retreated, and the latter, 

 again, form a double line of supplementary cliffs at the back, the first consisting 

 of the mottled clays, and the second by the more recent clays, finished off by a 

 travertine capping. 



The Pliocene bed is about 5 feet in thickness, and, as a rule, calcareo-siliceous. 

 It is sparingly fossiliferous, locally, except on some planes in the bedding, 

 when the whole surface of the rock may be covered by internal casts of mollusca, 

 mostly of small bivalves, sometimes masked by a mineral coating. At one out- 

 crop were collected such typical forms as Spondylus arenicola, Tate; Laganum 



