280 



SUB-SECTION A. 



BRIGHTON (BORE) TO BLACK POINT (4A MILES). 



The township of Brighton is situated near the southern boundary of a great 

 faulted earth-block which has had a downthrow of at least 4,000 feet. A great 

 pit of such a depth would have existed where Adelaide stands had it not been 

 filled up to the extent of over 2,000 feet, partly by deposits from repeated incur- 

 sions of the sea, and partly by the perpetual wash of clay and stones from the 

 higher ground. 



The Adelaide platform (which forms one of the ledges in the successive 

 subsidences of the ground towards the centre of the great rift-fault of the Gulf) 

 is in the form of a curve, having its convexity towards the hills with a south- 

 westerly trend that reaches the coast at the Marino Rocks. This westerly curve 

 of the hills to the sea supplies very definite evidence of earth fracture. Had 

 this curve in the hill country been caused by a tectonic twist it would have 

 changed the strike of the beds and the Mitcham quartzites would have been 

 continuous in outcrop to the coast. But this is not so ; the strike continues in 

 an approximately north and south direction, and newer beds in the succession 

 form the outcrops to the coast, being truncated and cut ofif on their northern 

 edges by the faulting. 



A boring for water at the Institution for the Blind, Deaf, and Dumb, a 

 little north of Brighton township (Sec. 238), carried out by Morrison, Gray 

 and Co., passed through alluvium to a depth of 223 feet, when, after 2 feet of 

 limestone, the bore entered "marine limestone with shells," which was penetrated 

 to a further depth of 79 feet. Another bore, situated a little to the southward 

 of the above mentioned, on the grounds of late Rev. A. Macully, passed through 

 similar beds. The material was sandy (mostly unconsolidated) and carried an 

 abundance of the large foraminifer, Operculina complanata, which is a very char- 

 acteristic fossil in the Muddy Creek beds, Victoria. Age: Janjukian (Miocene). 

 As a bed of fossiliferous Lower Pliocene (Kalimnan) occurs on the scarp of 

 the older rocks, within a short distance to the southward of Brighton, and at a 

 height of 40 feet above sea level, the throwdown of the Brighton section is 

 thereby evidenced, and probably represents the same faulted segment that was 

 proved in the Croydon bore. 



The foreshore between Brighton and Seacliff (about a mile) forms a long 

 slope with shallow water to seaward and bounded, on the landward side, by low 

 sandhills that rest upon a floor of recent clay a few feet above sea level. This 

 clay floor bears up the drainage from the sandhills, giving rise to a series of 

 springs near the base of the clififs on the seaward side. 



At Seacliff, the clay beds displace the sandhills and form the main clififs. 

 At the latter township a road has been cut down through the alluvial beds to 

 the beach, giving a complete section of the same ; mottled clays and gravels at 

 the lower levels, and newer reddish clays on top. CliflFs of this type continue 

 for more than a mile. There is a low platform between the cliffs and high- 

 water mark, varying from 50 yards to 100 yards wide, and is built up of similar 

 materials to that of the cliffs. There are no evidences of marine exuviae on 

 this flat, which appears to have been formed by the action of the rain on the 

 face of the clay beds together with small alluvial fans brought down by rivulets 

 which run during seasons of rain. 



About a quarter of a mile to the southward of Seacliff railway station 

 there is a very extensive washout, caused by a very small runner that has 

 excavated a canyon, having vertical sides of over 20 feet in height. This work 

 of erosion has been accomplished within the years of European settlement. 



