62 THE ORIGIN OF AUSTRALIA 
the deterioration of the climate consequent upon the death 
of the Opal Sea. The central portions of Australia were 
converted, in fact, into a huge sand-bath. This idea I 
have elaborated somewhat in my recent work, ‘“‘ The Story 
of the Noble Opal,” and shall further develop in a forth- 
coming work on ‘‘ The Origin of Australia.” It suffices to 
point out that one may say scientifically as well as epi- 
gramically that the Opal and the Kangaroo have a common 
origin. 
27. The Opal Sea must have been much like what its 
present representative, the Arafura Sea, is now—so shallow 
that it is rather submerged land than ocean. One can 
anchor anywhere between Australia and New Guinea, 
and there is no really deep water between there and Borneo 
or the mainland of Asia. But the Opal Sea was not ob- 
literated by infilling of sediment—elevation had much to 
do with the process, which was not completed until Tertiary 
times, an additional reason why the term Cretaceous Sea 
is imappropriate. The elevation was most rapid in the 
north, so that at an early date the cooler southern waters. 
were cut off from what is now Central Australia. The first 
union of Australia Orientalis with Australian Vera was to 
the north—and to this day, the continent, as a whole, 
slopes downwards north to south. 
28. Of the Tertiaries it is only necessary to speak in 
general terms. They prove that elevation continued till 
Australia became a continent, and widely distant Jand- 
and fresh-water deposits, from the extreme north to Tas- 
mania, with beds in many places rich in plant remains, 
show how different the flora was from that which now occupies 
the area, and stranger still, prove that, as yet, no land 
mammal has reached even Australia Orientalis. What 
these geological conditions tell us of the old climate we must 
now proceed to unravel. 
Wi. THE CLIMATE OF THE AUSTRALIAN 
ARCHIPELAGO. 
29. That the climate of the old Australian Archi-. 
pelago must have been very different from the present arid 
conditions is almost self-evident. Picture the state of affairs. 
A long, narrow, mountain land in the west, singularly lke 
