908 The American Naturalist. [October, 
east and west a few miles to the south of Lake Eyre. It then makes 
southeasterly for Barrier, and taking a long sweep to the east and north 
embraces the extent of those rivers that flow from south of the Gulf of 
Carpentaria into Lake Eyre. The shape is semicircular, and crescent- 
shaped, extending towards a half moon. No doubt detritus from the 
extensive area covered by the already-mentioned red sandstone forma- 
tion contributed largely towards filling it up to a level much higher 
than the present level of the country ; this is easily seen by the numer- 
ous tent-hills and table-lands scattered throughout the area of the 
basin, ranging from 200 to 500 feet high, of which Chamber’s pillar is 
aremnant. As the basin sank, or surrounding land became elevated, 
so the flood waters carried this newer Cretaceous formation to the lowest 
depression, cutting deep gullies and wide waterways through the newer 
deposits, and generally lowering the basin. This has been going on 
probably from time immemorial ; certainly from Cretaceous (second- 
ary) age, down through Tertiary and Quaternary ages to the present 
time. When the seas that washed the softer and newer deposits away 
from the Macdonnell ranges and laid bare much of the primary rocks 
had subsided, and Central Australia was elevated quite above sea-level, 
and long ages of scorching summers had evaporated its larger lakes and 
surface waters, and the Cretaceous age (during which Lake Eyre was an 
inland sea) was rapidly becoming a thing of the past, a newer influence, 
and one that exists to-day,—viz., that of the wind,—probably blew 
into all secluded and rock-bound spots, depressions, shallow lakes, and 
like places the sandy weatherings from around their base, and a newer 
formation was the result. This is the commonly called ‘desert sand- 
stone,’ for what reason I have never had a satisfactory explanation. 
oth as a shallow-water deposit and a dry wind-blown deposit it 
retains its unmistakable characteristics. Its color is that of an ordi- 
nary grindstone, and it consists of horizontal layers, the cap of each 
being harder than that underneath it. By weathering its sides get 
hollowed out, and in the caves thus formed the aborigines find a refuge 
from the extremes of weather, often painting devices on the walls. 
“ The great extremes of heat and cold, a dry atmosphere, and strong 
winds caused through radiation, tend to constant degradation of the 
rocks, the detritus being blown into sand-hills and distributed through- 
out this large area. In Western Australia, along the line of route taken 
by the Hon. John Forrest, surveyor-general of Western Australia, in 
lat, 26° S., a sandstone is met with that covers all other rocks from E. 
long. 122° to E. long. 126° 30’. In this extensive area of ‘desert 
sandstone’ all the rising ground is composed of it. ‘Very often one 





