28 
The Queensland Naturalist. 
May, 1927 
Another evidence of recent though smaller elevation 
occurs in the Brisbane River and neighbouring streams, 
such as Kedron Brook and the Pine rivers. This is the 
existence of well marked terraces of alluvium above any 
possible reach of flood at the present time. They show 
that the streams had formed alluvial flood plains in their 
valleys, and that an elevation of the land had compelled 
them to lower their beds till the grade was readjusted to 
the new levels. These terraces can be recognised almost 
to the heads of the streams. 
One feature of the Brisbane River attracts attention 
on the merest glance at the map. From the head of the 
“Western branch/’ near Nanango, down to* the vicinity 
of Ipswich, the main stream twists and turns about from 
side to side of a nearly straight line some eighty miles 
long. The direction of this is N.N.W.-S.S.E. No chance 
occurrence in the development of a stream could give 
rise to such a thing; it must be due to a linear folding 
or faulting of the earth’s crust. Geologists have shown 
on the western side of Ipswich a very large fault, which 
runs N.N.W.-S.S.E. It has been mapped by the Geological 
Survey as far north as Northbrook, and it k> in line with 
and indeed coincides with part of the axial line of the 
upper Brisbane. 
There is thus very good reason for thinking that 
the course of the river was determined by this great 
earth movement, an association the knowledge of which 
may some day be of service in elucidating the age of 
both. 
Probably the movement was sufficiently rapid to alter 
the course of the then existing deep-cut streams, but 
possibly the country was nearly flat like much of our 
present-day West, and the movement merely caused a 
shallow' straight valley in the position in which the river 
has since remained. It might be suggested that the fault 
merely determined the outcrop of harder rocks on its 
eastern side, and that the stream was held bv these to 
a course along their margin. Certainly from Northbrook 
right down to Indooroopillv the river turns from side to 
side across the boundary of the schists and mesozoic sedi- 
ments, but its meanders lead it into the hilly schist 
country as readily as into the softer and less hillv 
mesozoics, and we shall consider later two examples of 
smaller streams cutting gorges through mountains of very 
hard rock instead of making slight deviations to avoid 
them. 
