311 



can be seen working inwards by cracks and joints, the margins of such crevices 

 being blanched, while the inner portions, between the cracks, retain their original 

 black colour. 



The Cambrian slates appear abruptly in the cliffs of the sea coast, on the 

 southern side of the great alluvium deposits, in cliffs of about 150 feet in height. 

 Juvenile features are present in the form of narrow gorges and two waterfalls 

 in the slate. One of these has a fall of 80 feet, broken by a ledge after the first 

 20 feet. These waterfalls have probably been "hung up" by reason of the some- 

 what rapid retreat of the cliffs, or by faulting and downthrow towards the "rift." 



The Cambrian beds forming the sea-cliffs, and for some distance inland, 

 are extraordinarily fractured. There is close jointing in all directions, and what 

 appears to be master-jointing, or slide faces, occur nearly parallel with the coast, 

 with the result that there are very heavy and extensive landslips down to the 

 beach, leaving smooth faces from which the masses have slipped. The Cambrian 

 slates adjacent to the disturbed Tertiary beds have evidently been influenced by 

 the same tectonic movements and have received a throwdown to the north-west, 

 producing also a local system of jointing and intimate fracturing. 



GENERAL REMARKS. 



DiSCONFORMITY BETWEEN THE UpPER AND LoWER MaRINE SeRIES. 



In addition to the palaeontological evidence for an hiatus having existed 

 between the deposition of these respective sediments there are certain physical 

 considerations that point in the same direction, as stated below : — 



1. A slight stratigraphical unconformity can be detected at Blanche Point 

 and elsewhere. 



2. The Miocene, or Lower Marine System, has a much wider geographical 

 range than the Pliocene, or Upper Marine System. 



3. The Pliocene sediments are not always coincident in their occurrence with 

 the Miocene. Thus: (1) The Pliocene sometimes rests upon the Miocene, as in 

 the metropolitan area, in sea-cliffs from Blanche Point to Snapper Point, in the 

 cliffs of the River Murray, and in the sea-cliffs of Edithburgh. (2) It rests 

 on the Permo-Carboniferous glacial beds at Black Point. (3) On a ( ?) Pre- 

 Pliocene sand rock at Hallett's Cove and in the lower cliffs to the northward of 

 Morphett Vale Creek. (4) In several instances it rests directly on the Cambrian 

 beds, as at Marino, also a mile inland from Hallett's Cove, and on the top of the 

 sea-cliff (purple slates) a little north of Rocky Point. 



4. The Miocene System has been subjected to more extensive deformation, 

 chiefly by faulting, which has caused a wider range in the matter of elevation 

 than has been the case with the newer system. 



It seems probable that after the thick sedimentation had taken place over 

 most of southern Australia, during Miocene times, the sea retreated, on the 

 elevation of the land, to the southward, and after a time made a brief return 

 over a portion of its former area, and was then limited to shallow water that was 

 especially productive of oysters. 



The sediments laid down during the second incursion of the sea were of a 

 calcareo-arenaceous nature. When the sea once more retreated, the calcareous 

 portion of the sediments, under semi-dry conditions, was drawn to the surface 

 and precipitated as a surface limestone which now forms the craggy, unfossili- 

 ferous limestone that overlies the fossiliferous sandstones. 



The ( ?) Pre-Pliocene Sand Rock. 



The peculiar sandy and clayey bed, of a whitish colour, that underlies the 

 Lower Pliocene, in places, presents some difficulty in relation to its strati- 

 graphical position. At Hallett's Cove it is absent from the section on the Black 



