August, 1934. 
The Queensland Naturalist. 
35 
wood, Beaudesert and Darling Downs. Into these Walloon 
strata there have been intruded a great variety of igneous 
rocks, both of the light-coloured trachytic and the dark 
heavy basaltic types, in the form of plugs, dykes and sills. 
Upon the sediments there have been extruded volcanic 
ashes or tuffs, as well as enormous thicknesses of basaltic 
lava. In the Main Range there is a thickness of up to 
3,000 feet of volcanic material on top of the sandstone ! 
In spite of this evidence of intense and prolonged 
vulcanicity, the Walloon strata usually show only gentle 
dips though sometimes steeper dips do occur. The most 
notable disturbance of the strata is probably that seen on 
the western side of Mt. Alford, above Moogerah school, to 
which attention was called by Mr. S. B. Watkins. Here 
an outcrop of sandstone, in character more like the Bun- 
darnba rather than the usual Walloon sandstone, has the 
bedding tilted to vertical, with the strike in a north-east- 
south-west direction. From its appearance this must re- 
present an important fault line, curiously enough in a 
direction at right angles to the Main Range. Like other 
big geological faults in south-eastern Queensland, this 
fault does not appear to have any direct effect on the pre- 
sent surface levels. 
Owing to their greater hardness and resistance to 
weathering the igneous rocks, and especially the trachytic 
rocks, give rise to the many isolated mountains of the dis- 
trict which give it its picturesque charm. Mt. Edwards is 
composed of trachyte, and through it Reynolds Creek has 
cut the remarkable gorge which forms such a surprising 
contrast to the wide valley both above and below. This 
gorge gives us the clue to the development of the present 
drainage system and topography of the region. Reynolds 
Creek rises in the Main Range about twelve miles away, 
and continues on in the same direction after passing 
through the mountain. On the map the creek appears to 
take no notice whatsoever of the 2,000 feet trachyte mass 
situate right on its course, although a comparatively small 
deviation would have avoided it. 
Now we know that trachvte is very resistant to de- 
nudation. and remains as bold hills when the surrounding 
softer rocks are denuded away. The Mt. Edwards mass 
probably represents the core of a volcano. Whether as a 
volcano, or after subjection to denudation, it must have 
formed a prominence, not the bottom of a valley. When 
Reynolds Creek started its career it would have followed 
some depression, shallow or deep, and there could have 
been no mountain to obstruct its course, and prevent it 
from pursuing the even tenor of its way. It must, there- 
