7<J The South Aiistralian Naturalist. 



Mr. Chapman has now made some of his results available in a 

 more popular form in a paper on the geology of the Mallee, 

 published in the current number of the "Victorian Naturalist.'' 

 Regarding the water problem, Mr. Chapman mentions that 

 during 1919 103 bores were put down by the Government of 

 Victoria, 100 of which struck fresh water at depths varying 

 from 150 to 700 feet ; in three bores the water was artesian, 

 that is, flowed out at the surface, whle in the remainder pump- 

 ing would, of course, be necessary. The chief water-bearing 

 beds are of Miocene age, and contain limestones rich in polyzoa. 

 From a knowledge of the fossils that occur in regular succes- 

 sion as we descend through the Mallee beds, it is now possible 

 (through the Avork of Mr. Chapman) to determine approxi- 

 mately the position of the water-bearing series. This is of very 

 great value, as instanced by the case of a New South Wales 

 engineer, who was recently making enquiries in Melbourne as 

 to the prospects of striking water in a partly-worked bore. 

 He had wisely brought with him a few shells from the lowest 

 bed reached, and these, when examined by an expert, pro- 

 claimed the exact position with regard to the water-bearing 

 beds. 



The surface accumulations of the Mallee consist of reddish 

 loose sands, travertine limestones, freshAvater limestones, soapy 

 clays, and deposits of gypsum and rocksalt. A fairly constant 

 feature is a blue clay-band at varying depths, of shallow marine 

 origin, and fiom Lpwer Pliocene to Upper Miocene in age. 

 ''This bed, probably extending through the greater part of the 

 Mallee, tends to hold up the brackish water, on account of its 

 impervious character." so that brackish water is usually met 

 with above the blue clays, but these beds must be penetrated 

 before the real freshwater beds are reached. 



The varying deposits found in the bores point to quite 

 varied climatic conditions in the past in this area. The brown 

 coals of Moorlands (S.A.) and Tiega (Vic.) show that certain 

 portions of the country then produced a luxuriant growth of 

 timber. The type of animals found in other beds shows that 

 at one time a warmer climate prevailed than is the case at 

 present, while in yet other cases desert conditions are sug- 

 gested. During the marine period chalky limestones to a 

 thickness of over 2,000 ft. were deposited, but this sea slowly 

 became shallower, until finally the sea-bottom emerged as dry 

 land. Since then dune, lake, and swamp have prevailed, while 

 in the wetter areas arovmd Mount Gambler there is a develop- 

 ment of the early stages of drainage by dolines and sink-holes. 

 There is evidence, says Mr. Chapman, that in the past, but 

 subsequent to the final uplift, there was a more copious rainfall 



in the Mallee areas than there is to-day. 



' ' Tellurian, " in " The Augtralasian. ' ' 



