1883. ] The Geology of Central Australia. 1129 
probably been dry land since the close of the Mesozoic ; at least 
there is no evidence of its having been submerged. As the land 
arose the rate of elevation varied, occurring more rapidly in some 
places than in others. Consequently the interior sea would be 
changed first into an archipelago and this changed slowly into 
dry land, containing small inland seas, which gradually became 
large lakes such as Lake Eyre, Torrens and Gairdner. During 
the early half of the Quaternary the climate was moister, and con- 
sequently was better adapted for animal and vegetable life than at 
the present day. That it was the case is shown by the greater 
thickness and structure of the lower alluvial deposits, and also by 
the bones of the great marsupials found in them. These animals 
must have had a more luxuriant vegetation to feed upon than 
now exists. The climate probably, through the elevation of the 
southern border and other causes, gradually became more and 
More arid until it reached the present stage. The giants of 
earlier days have passed away, and strangely enough, as if nature 
delighted in abrupt antitheses, they are replaced by some of the 
smallest forms of the order of animals so characteristic of Aus- 
lia. 
Although the whole of this region is remarkably arid, the sur- 
face is intersected by innumerable watercourses which, though 
dry for the greater part of the time, periodically are filled by 
-water from the ranges. In the eastern part of the basin 
these creeks arise on the slope of the Queensland cordillera and 
flow westerly into Lake Eyre. From the north-west flow the 
Peake, Neales and others. Smaller creeks flowing in the same 
Seneral directions are abundant. They either die out altogether 
or unite with the larger ones, or end in the salt lakes so common 
throughout the region. The salt lakes are generally but little more 
than large clay-pans where the water has periodically accumulated 
and then evaporated, leaving a deposit consisting of various salts. 
Some, however, are larger, and like those I have mentioned, are 
true lake basins. The true lakes are never I believe, completely 
dry, but the water becomes very low and intensely salt and bit- 
ie Every flood as it comes down spreads out on the flats bor- 
dering the creeks, and extending laterally, in some places several 
Miles, quickly evaporates, leaving a deposit of earthy sediment, 
and finally a thin deposit of the salts. This process is repeated 
time and again until considerable beds are formed. If the flood 
