416 T. W. E. DAVID. 
tion where it rests with strong unconformability on Paleozoic 
Rocks, or even where resting conformably on Lower Mesozoic 
Rocks, should not consist largely of gravel and coarse sand. In 
many parts of Queensland, and possibly in portions also of New 
South Wales, there is a conformable upward passage from the 
strata of the Trias-Jura to the Rolling Downs Formation, and in 
such cases the sand and gravel beds will as a general rule be found 
to be very much thinner than in the case of the unconformable 
junction just mentioned. 
During the whole of the Rolling Downs Period large rivers, 
flowing from east to west, must have entered the margins of the 
Cretaceous Ocean, and must have spread their gravels over exten- 
sive areas, and these rivers, in New South Wales at all events, 
continued to flow down to the present time, their channels of 
course being subject to oscillations of position and various modifi- 
cations, as one geological period succeeded another. It cannot of 
course be affirmed that such rivers as the Dumaresq, the Gwydir, 
the Namoi, the Castlereagh, the Macquarie, and the Bogan were 
represented in Cretaceous times by rivers flowing in approximately 
the same latitudes as these modern rivers, but it can confidently 
be affirmed that in all probability several rivers, of which the 
above mentioned are the modern equivalents, must have existed 
in Cretaceous Time and have drained westwards into the Cretace- 
ous Ocean. Extensive gravels, must therefore, have been con- 
tinuously in course of deposition from early Cretaceous Time until 
the Present, and unless the latitude of the main valleys has altered 
since Cretaceous Time, the gravels belonging to successive geological 
periods must in places be superposed on one another, and so they 
would afford means of ingress for large bodies of water, which 
sink through the older gravels forming the channels of the modern 
rivers above mentioned, It is probable then, that a considerable 
amount of water finds its way into the artesian beds of the Rolling 
Downs Formation through percolating through ancient river 
gravels. There certainly is a considerable difference in the amount 
-of water discharged by these rivers near the foothills of the Main 
