15 
PHYSIOGRAPHIC NOTES FROM THE UNI- 
VERSITY OF WESTERN AUSTRALIA. 
THE PHYSIOGRAPHIC ELEMENTS OF THE SWAN 
COASTAL PLAIN. 
By W. G. W oolnougHj D.Sc., F.G.S., Professor of Geology. 
( Bead 13/7/ August, 1918.) 
The city of Perth stands upon the banks of the Swan River , 
here a mature stream il owing across a sandy plain some twenty miles 
in width. This plain has been described as the Swan Coastal Plain 
by Jutson in his comprehensive account of the Physiography of the 
State.'* 
The author desires to point out some details in connection with 
the structure to which attention was not drawn by Jutson in his more 
general account. On the east the plain is bounded by the scarp 
forming the western boundary of the Darling Peneplain.! 
Between the laterite-capped summit of the Darling Peneplain 
and the reefs of Rottnest Island, Garden Island, etc, the author 
believes that at least a dozen distinct physiographic elements may be 
recognised. (See Fig. 1.) 
(a.) The summit level of the Darling Peneplain. 
This rises to a remarkably uniform level of about 800 feet above 
sea level and extends almost without variation in character for at 
least 200 miles in a north and south direction. It is capped by lat- 
erite and is intersected by deep youthful river \ alleys, carved out 
of it since its upheaval. 
(h.) The edge of the Darling Peneplain is formed by a sharp 
escarpement, the “Darling Scarp,” due, proximately, to the under- 
mining of the hard laterite capping by the forces of erosion. While, 
as Jutson has pointed out, this feature is a fault scarp, the present 
edge of the plateau is not coincident with the actual fault plane, 
but has retreated some distance to the east of the earth-crack as a 
result of erosion. 
(c.) West of the cliff-like edge of the laterite capping is a hill 
slope, generally fairly steep, leading down to the edge of the plain 
itself. This element we may call “the Foothill Zone” On these 
foothills are exposed the basement rocks of the Peneplain, chiefly 
granites in great variety, seamed with dyke-like masses of basic and 
ultrabasic intrusive rocks, mostly somewhat recrystallised. From 
fLoc. cit., p. 42, 43, where references to previous literature are a-iven. 
