88 
The Queensland Naturalist May, 1938 
clearly if one compares the logs of the many bores put 
down in the neighbourhood of the Grey Street and Story 
Bridges. Thus a dredge may have to move only a few 
\ards in order to procure gravel of a different consist- 
ency or a higher proportion of sand. Mr. Fison cited 
one particularly interesting contrast in the bottom de- 
posits. At the point known as The Race (the Moggill 
Ferry is close by), the river flows through a deposit of 
almost pure sand, while both above it and below at no 
great distance are heavy gravels. Again, Mr. Voller in- 
forms me that there is a bank of very large boulders near 
the right bank of the river, opposite the Indooroopilly 
Golf Links, that is almost in the heart of the area from 
which the commercial gravels are obtained. 
One other point concerning distribution should be 
noted, namely, that the content of mud suddenly in- 
creases below the junction of the Bremer River with the 
main stream. This will not be surprising to those who 
have compared the pellucid waters of the Upper Bris- 
bane with the dirty opacity of the tributary stream. 
Now let us consider for a moment the depth of these 
deposits. Naturally, our knowledge of this aspect is 
most definite in that part of the river that flows through 
the city. As a result of the building of bridges, wharves 
and warehouses, a good deal of information has aecumu 
lated. Thus it is known that the piers of the Grey 
Street Bridge penetrate unconsolidated river deposits ta 
a maximum depth of 105 feet below low water before 
encountering solid rock, while those of the Victoria 
Bridge extend nearly 90 feet to their foundations from 
!he same datum Similarly, in boring for foundations 
on which to rest the main southern pier of the Story 
Bridge at Kangaroo Point, incoherent semi-consolidated 
material was pierced to a depth of 133 feet below low 
water level before rock b ottom was obtained. Such 
thicknesses seem to be normal for the river in this part 
of its course. Here and there the scour of the stream 
has been sufficiently strong to keep the bottom free from 
silt, and in these places a great depth of water is found. 
Thus at the sharp bend opposite the Botanic Gardens, 
near where the South Brisbane Coal Wharves stand, the 
river is 78 feet deep, while at the next sharp bend oppo- 
site Kangaroo Point, the rock bed is exposed nearly 100 
feet below the river level. 
With regard to the thickness of the deposits farther 
upstream, we have less definite information, but we do 
know that the central pier supporting the Indooroopilly 
