BY W. H. BRYAN, B.SC. 145 



the Brisbane River — or. rather that part of it above Oxley 

 Creek — which follows approximately the line of junction 

 between the Brisbane schists and the Ipswich measures, 

 really marks a series of fault-lines. A number of facts 

 seem at first rather to support such an idea ; for example, 

 the abrupt way in which the ranges rise out of the surround- 

 ing country and the fairly level summits of these ranges. 

 The writer, however, has found several objections to such 

 an hypothesis, and believes that the various phenomena 

 can be better explained as the result of differential erosion. 



At a point on the right bank of the Brisbane River 

 near Corinda, a section can be seen well exposed at low- 

 Avater showing the Trias -Jura beds resting unconformably 

 on the Brisbane schist, and moreover, this section lies in 

 the line of supposed faulting. The very gentle dips of the 

 Ipswich beds in close proximity to the supposed lines of 

 faulting seem also to militate against such an idea, at least 

 for the area under discussion. The chief points in favour 

 of the hypothesis that Taylor Range and Enoggera Range 

 are residuals resulting from differential erosion are, first, 

 the fact that these Ranges are composed of very resistant 

 rocks — the granites, and schists strengthened by large 

 intrusions — and second, the marked parallelism of the strike 

 of the intrusives and the axis of granitic intrusion with the 

 directions of the ranges and chief spurs. In this connection 

 it is interesting to compare the Geological Map (Plate XI.), 

 with that of the Physiographical features (Plate XII.) 



iv. — The Rocks of the Area. — General. 



In the geological formations of the area, rocks of both 

 igneous, sedimentary and metamorphic origin occur. The 

 first are represented (1) by rocks of a granitic type — the 

 Enoggera granites ; (2) by intrusive bodies — mostly of a 

 rhyolitic facies, but in part made up of a more truly 

 hypabyssal type ; and (3) by flows and sills of a basaltic 

 nature. It is Avith the first and second of these classes — 

 which are probably closely related — that this paper is chiefly 

 concerned, while such examples of the third class as occur 

 in the area dealt with are dismissed with this brief notice. 



