46 



THICKNESS 

 IN FEET. 



1. " Eecent Marine," cliiefly sands, containing sea shells 



of existing species to a depth of ... ... ... 66 



2. " Pliocene Drift." Judging from lithological features, 



the upper 161< feet undoubtedly belong here. The 

 underlying 100 feet, however, which consist of clays 

 and carbonaceous muds, have no parallel in the more 

 superficial deposits of the Pliocene Drift, to which 

 our knowledge is limited. But in the absence of 

 palaeontological evidence to the contrary, they must 

 be relegated to that period ; though they have a 

 strong resemblance to certain fluviatile Miocene 

 deposits, which they may well do, as they were pro- 

 bably accumulated under similar conditions ... ... 264 



8. " Pre-Silurian." Clay-slates, more or less micaceous, 



throughout to ... ... ... ... ... ... 435 



Total ... 765 



Expla:nations to Section, Plate TV., Pia. 2. 



The surface line represents the chief gradients on the railway, 

 and therefore omits the minor undulations. 



The section is in the line of true dip, bearing 8° S. of east. 

 It traverses the cutting at the 11^ milepost, and crosses the 

 railway on the marsh at the fifth milepost from Port "Wakefield. 

 The horizontal scale is one inch to one mile, and the vertical 

 one inch to 400 feet. 



The horizontal distance between the extreme outcrops of the 

 Pre-iSilurian is li miles, and therefore with an average dip of 

 40° represents a vertical thickness of 3429*6 feet. 



The lowest stratum exposed is a micaceous sandstone ; then, 

 in the cutting at 13| miles there are thin-bedded quartzites, 

 and coarse and fine-grained felspathic grits. Thence most of 

 the section is occupied with mudstones — i.e., argillaceous rock 

 showing no lamination, exceedingly tough, but on exposure 

 breaking up into cuboidal pieces. These mudstones have occa- 

 sionally intercalated among them thin bands of quartzites and 

 hard sandstones. 



The uppermost stratum is a flinty quartzite, bedded and 

 strongly jointed, having a thickness oi* 660 feet. It constitutes- 

 the flank of the Hummocks Eange, and occupies the whole east 

 front of the hill of the South Hummocks. 



Passing over the summit level of the railway line, the Pre- 

 Silurian rocks are hidden by a covering of loam, having a 

 travertine crust, and lU) other rock exposures are seen for the 

 rest of the distance to "Wallaroo. 



