260 



certain area so effectively as to practically exclude all com- 

 petitors and to maintain the exclusive possession for a 

 considerable time; yet, notwithstanding its local fecundity, 

 failed to establish itself beyond its own particular province. 

 The deposit, as seen on the railway, is intersected by a 

 shallow valley, which cuts it in two. The outcrop must at 

 one time have been continuous, but whether it has been 

 eroded to its base by the valley or simply obscured by cover 

 in the hollow is uncertain. The permanent way has been 

 ballasted with the shells throughout the two cuttings, and 

 the embankment between the cuttings has been constructed 

 of the same material. The full length of the fossiliferous 

 outcrop, including the intervening valley, is about 500 yards. 

 The travertine limestone which caps the fossiliferous bed 

 slopes, with the ground on either side of the rise, and together 

 with the shell-bed, pass below the surface of the ground. 

 At no point in the outcrops is the base of the fossiliferous bed 

 seen, nor the bed-rock on which it rests ; its thickness, there- 

 fore, is uncertain. 



Evidence of Earth Movements. 



It has been already stated that the normal height of the 

 Upper Cainozoic marine series in South Australia is 100 feet 

 above sea-level, or less than that. At Hallett's Cove they 

 occur in two steps, at 100 feet and also at 200 feet above 

 sea-level. The height of the Mount Mary railway station 

 is given, officially, as 311 feet above sea-level, while the fossili- 

 ferous bed in that neighbourhood is 30 feet higher. The 

 corresponding bed in the cliffs of the River Murray is thirteen 

 miles distant from the Mount Mary bed, and has a mean 

 elevation of 40 feet above present sea-level. The two occur- 

 rences are, therefore, not only widely separated as to location, 

 but the one occupies a position 300 feet above the other. 

 Notwithstanding these discrepancies in their present positions, 

 there can be no doubt that the respective beds were deposited 

 at the same level, and that the oysters formed a living colony 

 in the same w 7 aters and at the same time. 



In order to explain the present discordance in their 

 respective levels, it must be assumed that a two-fold move- 

 ment has taken place. First, a general uplift of the sea-bed, 

 extending to some hundreds of feet, by which a plateau was 

 formed ; and, secondly, a collapse on the eastern side, by 

 which the ground in that direction subsided to the extent of 

 at least 300 feet. 



The facts brought to our notice by this interesting outlier 

 of marine beds at Mount Mary form an additional contribu- 

 tion to the geological history of the Mount Lofty Ranges, 



