WATER SUPPLY IN THE INTERIOR OF NEW SOUTH WALES. 89 
particular channel, is proved, I think, by the following table, which 
gives the excavating power of currents of different velocities :— 
Inches per Miles per 
second. hour. 
3 0°170 will begin to work on fine clay. 
6  0°340 will lift fine sand. 
0°4,545 will lift sand as coarse as linseed. 
ill sweep along fi vel, 
24 1°3,683 will roll ae pebbles an inch in diameter. 
36-20 i angular stones the size of an egg. 
(D. Stephenson, Canal and River Engineering, p. 315.) 
The current of the Darling River with a fall of only a few 
inches per mile is from half a mile to more than a mile per hour, 
is at least 2 feet per mile, and probably for the first 100 miles 
more than 3 feet, so that with such a fall these creeks would, as 
the above table shows, have been able to maintain and deepen 
their channels, if they ever had had any. The larger creeks or 
rivers which have, by reason of the great quantity of water carried 
down from the mountains, succeeded in cutting defined channels 
through the plain, and reached the lowest level to form the Dar- 
ling, have one peculiarity which, without exception, is found in 
them all. From the point at which they leave the mountains 
they have no defined valleys, although above that point the valleys 
are well defined, and must have taken ages to cut out. All the 
t 
rivers, and yet with a fall of from 2 to 3 feet per mile, and a cur- 
rent of 3 or 4 miles per hour, as some of them have, we should find 
many signs of long continued erosion unless, as I suppose, the 
country had by some agency been rendered so flat in the cross see- 
tion of the river courses that the most of the water always spread 
out over the country. The older and harder strata on which the 
clay beds rest are not level, as is shown by the various depths at 
which they are reached in sinking wells, therefore it seems clear 
that if the present rivers, with the current which they would have 
had with a fall of 2 or 3 feet per mile, had ever flowed along this 
uneven bottom formation, they never could have built up an even 
plain with a general level extending over hundreds of miles. 
Besides the fact that these clay-beds and sand drifts with nearly 
horizontal stratification are found in places hundreds of feet below 
re con f signs of the 
courses of the Namoi, Castlereagh, M 
impossible to say where the watershed of one river ends and that 
begins. There is a 
of the next |} is a remarkable sameness about the 
