44 



at tlie close of the Miocene epoch, in a similar way to that 

 which took place at or near the close of the Pliocene period. 

 Though the evidence be somewhat defective, I will here state 

 that the beds known as the "Upland Miocenes" are partly o£ 

 marine origin, and partly flnviatile and a?olian. Therefore whilst 

 the beds were being added to the series by the influence of the 

 two last-named conditions, a vast difference in the temperature 

 of the Australian climate must have prevailed from what we 

 now witness. In the indubitable marine beds at Aldinga Bay 

 and the Murray Cliffs, the more delicate, or what we might 

 term the more tropical species of the fauna, gradually disappear 

 throughout the lower beds of the formation, until at either 

 place the uppermost fossiliferous bed in the series is entirely 

 restricted in its fossil remains to a species of oyster, and 

 that, too, I am credibly informed, is not at present an inhabitant 

 of South Australian waters. Thus a study of the marine beds 

 in question teaches — Eirstly, that as the cold was gradually 

 setting in, the molluscan species which are most indigenous to 

 tropical waters disappeared from our shores. At last even 

 the oyster, which is considered to possess a wider geogra- 

 phical range than many other of the molluscan genera, suc- 

 cumbed to the rigours of the increasing cold also. At both 

 localities the bed is overlaid by one known as the non-fossil- 

 iferous Miocene clays. These non-fossiliferous clays arose 

 from the azoic character of the waters of the surrounding seas 

 of the period ; and that the deposits of a sandy nature, found 

 sparingly distributed throughout the bed, are the feolian accu- 

 mulations of the period there can be little doubt. As the 

 deposits ascend in height above present sea level the seoliau con- 

 stituents become more prominent in character, until they reach 

 .an altitude of about 1,100 feet, when they become, so to speak, 

 the equivalents in time of the calcareo-argillaceous beds of the 

 Adelaide, Gawler, and other seaboard plains. 



I have been led to conclude that the whole deposit, in part 

 -sub-marine and in jDart sub-aerial, was formed whilst our earth 

 was passing through one of its periods of high eccentricity, 

 and consequently this change for the time being of the earth's 

 pathway round the sun would naturally lead, in certain lati- 

 tudes at given periods, to an excessive amount of rainfall, and at 

 •others excessive drought ; and such extremes of secular change 

 would also lead to a corresponding amount of geological disin- 

 tegration, and it was during such a period, as it seems to me, 

 that the non-fossiliferous Miocene beds in the neighbourhood 

 of Adelaide and other kindred Australian deposits were de- 

 veloped. 



TVhy the Seaboard Drifts of South Australia are Void of 

 Marine Fossil Remains. — Profound depths and varying tempera- 



