Jone, 1907.] THE VICTORIAN NATURALIST. 31 



If, then, the volcanic rocks represent a late stage in the great 

 volcanic outburst of Devonian times, it would appear that no 

 stratigraphical break exists here between the Devonian and 

 Carboniferous. It is therefore difficult to say where the one 

 stops and the other begins. Since it is at present impossible to 

 definitely correlate these Wellington lavas with those of the 

 Snowy River, it is suggested that they might be included under 

 the term Wellington rhyolites, while the term Avon series can be 

 well extended to include the overlying sedimentary beds of the 

 whole of the region. 



Ancient Plateau Valleys. — The plateau character of much of 

 our Australian geography has been referred to Uy many writers. 

 Dr. A. W. Howitt, in particular, has described the feature which 

 is shown so strikingly in eastern Victoria. In south-eastern 

 Australia broad earth movements of both uplift and subsidence 

 have succeeded from time to time, with intervening periods of 

 comparative stability. These successive movements have thus 

 intermittently affected the river system ; the uplifts mostly in the 

 direction of rejuvenating the streams. Various stages, therefore, 

 in the dissection of the plains and plateaus are well shown in 

 Gippsland. The broad alluvial plains, with their terraced banks ; 

 the dissected Cainozoic coastal plains ; the canyon-like courses of 

 the mountain streams, and the plateau remnants forming the 

 snow plains of our highest mountains, form a striking series, illus- 

 trating the evolution of the present contour. 



In some cases the nature and structure of the rocks have 

 been more favourable for the longer preservation of the 

 plateau or pene-plain character. This is particularly the case 

 in the area comprising the slightly inclined and durable i-trata of 

 the Upper Palaeozoic rocks, and also the basalt-capped elevated 

 areas, as in the Dargo High Plains. In the case of the latter, 

 remnants of the old river-beds are found high above the present 

 rivers and buried beneath the basalt fiows. In other areas 

 remnants of old river channels are to be found on the snow-plain 

 country at the source of many of the streams, and not yet reduced 

 to the grade of the present channels. Such instances are well 

 shown in the Wellington district. They are remains of old high- 

 level strike valleys which lie between well-marked scarps, and 

 continue in some cases as wide, open, well-grassed valleys for some 

 miles, and then drain out over a steep, rocky course into deep 

 canyon-like gorges. 



The influence of the geological structure of this area on the 

 evolution of its river system is well shown. The broad anticlinal 

 folding of this Upper Palaeozoic belt has produced a zone of 

 slightly inclined beds of varying hardness, consisting of hard beds 

 of conglomerate, sandstone, or rhyolite, with softer bands of 

 mudstone and shale. 



