234 



tion that these swamps possessed a special geological signifi- 

 cance, but in what way I could not tell. On examination it 

 was found that the water, spreading over the flats, was sup- 

 ported by an impervious clay, more or less stony, and that 

 this clay was overlain by a porous sandstone or loose sand, 

 often of considerable thickness. The origin of the swamps 

 was thus self-evident. The absorbent sandstone of the hills 

 stores the rain which ultimately finds it way down to the 

 clay-bed, and the latter, being exposed by denudation along 

 the lines of drainage, collects on its surface the waters oozing 

 from the banks and thereby causes a swamp. 



The very youthful characteristics of the present drainage 

 of the district cannot fail to attract the notice of the physio- 

 graphist. Not only is the. Mount Compass basin largely filled 

 with incoherent or soft material, but the main streams are 

 still flowing over soft clays on which, at present, they have 

 made but slight impression. It is true the absorbent pro- 

 perties of the superficial beds limit the denuding force of the 

 rains, and the rank growth of the swamps checks the move- 

 ments of running water, until erosion is reduced to zero, yet 

 it is remarkable that these ancient sediments of Permo- 

 Carboniferous age should exhibit such youthful features in 

 their present stage of erosion. Similar evidences are afforded 

 by the short, torrential streams which flow down the steep 

 sides of the Pre-Cambrian inliers, for these have but slightly 

 incised the sides of the hills they drain, and thereby register 

 only a relatively brief period since the removal of the pro- 

 tecting glacial deposits and the exposure of the older rocks 

 to atmospheric waste. 



The inliers of older rocks possess rounded outlines and 

 are lineal to the main valley as well as parallel to each 

 other. These features, together with the absence of spurs 

 from the sides of the ranges, establish a strong probability 

 that the topographical outlines of the older rocks were shaped 

 under glacial erosion. 



From the amount of glacial moraine still filling the de- 

 pressions of the Mount Compass district, as well as forming 

 parts of its watershed, it is difficult to define the main chan- 

 nels of the old Palaeozoic valley. The abundance of water at 

 or near the surface has made it unnecessary to sink deeply 

 for supplies, so that the thickness of the glacial clay has 

 not been proved. Judging by the outcrops of the older 

 rocks, the deeper parts of the Palaeozoic valley lie between 

 the Black Swamp and Currency Creek, for in this belt of 

 country the older rocks do not show at the surface. 



The regional subsidence of the southern portions of the 

 continent, in Post-Palaeozoic times, had the effect of reversing 



