86 
The Queensland Naturalist 
May, 1938 
isties of the pebbles making up the path, let us now go 
back one step in the history of the gravel and examine it 
as it emerges from the bed of the .Brisbane River. 
Through the courtesy of Messrs. William Collin and 
Sons, and their Supervisor, Mr. 0. J. Voller, I have been 
able to inspect samples of the gravel as it is dredged from 
the river, and to compare them with the gravel on which 
the above generalisations have been based. The “raw 
material” consists of an admixture ranging from coarse 
boulders twelve inches in diameter to the finest mud. 
But the extreme members of the series constitute only a 
very small part of the whole, tlie bulk of the material 
being made up of intermediate gravels and sands. After 
it has been unloaded from the barges, the occasional 
large boulders are removed by hand, the fine mud is 
washed away (and the product thereby cleansed) in a 
stream of water, and the remainder is separated by 
screens of suitable mesh into gravels of several grades of 
coarseness, “coarse sand” (which is, in fact, a very fine 
gravel), sand and fine sand. It was a medium grade of 
gravel cleansed and graded in this manner that found its 
way after a long and complicated history to my garden 
path. I was particularly interested to note that in spite 
of their artificial separation, this was clearly repre- 
sentative of the gravels as a whole. I did not notice any 
strange pebbles in the barges, and the proportions seemed 
much the same. It would seem that the quantitative 
separation of the pebbles did not bring about a qualita- 
tive separation, too. 
Although occasional large loads have been brought 
from higher up the river, nearly all the gravel used in 
Brisbane has been obtained from the bed of the scream 
between Six-Mile Rocks and Seventeen-Mile Rocks. 
Tremendous quantities have been gathered from these 
eleven miles, and the reach below the indooroc pilly 
Bridge has been particularly prolific. Mr. Voller in- 
forms me that at the peak of production a few years ago 
as much as 3,250 cubic yards were removed by the several 
operating companies in a single week, and that an 
average week at present produces about half that 
amount. When it is added that this activity has been 
proceeding steadily for many years, one can realise what 
a stupendous figure the total must be, and one can 
readily understand that suitable gravel banks are be- 
coming more and more difficult to find. 
In the early days of the industry many of the banks 
were emergent, in the form of small islands, and it was 
