92 
The Queensland Naturalist May, 1938 
granitic and allied plutonic rocks, there is no hint of 
this. 
Could one reconstruct the extensive shales and sand- 
stones of the Esk Series, the Ipswich Series, the Bun- 
damba Series and the Walloon Series by an examination 
of the sands associated with the pebbles of our gravel? 
I am sure one could not. In a search through several 
tons of pebbles, I have discovered only one fragment of 
carbonaceous shale — sole representative of several large 
coalfields. Could one visualise the great thickness of 
Bunya Phyllites from those occasional schistose frag- 
ments in the gravel which, having been reinforced by 
quartz veins, are sufficiently durable to form pebbles? 
I think not. Almost inevitably the softer, less coherent 
rocks would be under-estimated and misunderstood, and 
conversely, the hard and resistant rocks would be as- 
signed too great a thickness and too extensive an area. 
A study of the several degrees of rounding of the 
different pebbles would lead to similar half truths. Thus 
the relative angularity of the jasper pebbles points, quite 
rightly, to a not-distant origin. But it would be quite 
wrong to infer that the other more rounded pebbles 
come from a more remote source. Consider the position 
on the river a few miles above Mount Crosby. At this 
point the Fernvale Series, on the left bank, is shedding 
sharply angular fragments of jasper, while on the oppo- 
site bank the basal conglomerates of the Ipswich Series 
are providing the river with well-rounded pebbles ready- 
made. 
And yet in spite of such confusing things as these, 
the assemblage of pebbles found in the Brisbane Biver, 
or in any other river, has an individuality, a character, 
of its own, dependent on the history of the stream and 
the geological nature of the country drained by it. 
We are in a position to make a very strict test of 
this principle in the case of our own river. 
One of our field excursions last year was to Lone 
Pine, on the left bank of the Brisbane Biver. T was so 
interested in the geology of the spot, as seen on that 
occasion, that I returned there a few days ago. There I 
stood on a deposit of gravel some fifty feet above the 
present river, and watched a dredge at work bringing 
up other gravel from the river bottom. Surely one might 
be forgiven for thinking that two gravels so closely 
adjacent must be very similar, in spite of any difference 
in age or origin. But such is not the case. The Lone 
Pine Gravel (which is now mentioned for the first time 
