110 VOLCANIC ROCKS OF SOUTH-EASTERN QUEENSLAND 



III. PHYSICAL FEATURES. 



A general examination of the map of the area con- 

 cerned shows certain marked features with regard to the 

 drainage {see Plate X.). 



It is noticeable that ]MacPherson 's Range on the south, 

 and the [Main Range on the south-west and west, form 

 very definite water-divides. With respect to MacPherson's 

 Range, on the Queensland side all the drainage is to the 

 north and north-east, there being a marked parallelism of 

 the valleys. In fact, the characteristic feature is the 

 northerly trend of the drainage until the wider valleys in 

 the volcanic-rock-free portions of the Mesozoic measures 

 are reached, when there is a marked easterly trend. 



The main factor governing this northerly trend is the 

 general north and south direction of the ranges forming 

 the divide between the streams. An investigation of these 

 ranges leaves little doubt as to their being residuals, except, 

 perhaps, in the case of some of those in the western part 

 of the area. They are either at present capped with vol- 

 canic rock, or show signs of having been covered at one 

 time, and one is inclined to the belief that the pre-volcanic 

 drainage system had a general north and south direction 

 and that the north and south ranges of to-day mark the 

 sites of the former valleys, or else that, as a result of 

 folding movements, there was formed a series of depres- 

 sions extending in a general north and south direction. 

 The field evidence is very much against the latter. 



Wearne and Woolnough^ have shown that in Cainozoic 

 times the divide which is now constituted by the Main 

 Range was considerably to the east of its present position, 

 and that there are traces of several stream channels along 

 which the streams flowed in a westerly direction. 



The only evidence of extensive faulting is in the 

 western part of the area, and the same authors have shown 

 the influence of this which has resulted mainly in the 

 steep escarpment along the eastern slope of the Main 

 Range. 



» Proc. Eoy. Soc, N.S.W., xlv. 



