Rex T. PiiiDEii. 
loo 
jtlateau and tJins eoidiriiiatoi'y (‘vidcjieo of the Dai'liiig Raiill wliicdi lie Hup- 
poses is a stej) lault. l^hu'ther, in his arthde “Tiie p]iysiof»'raphic si;^’nilicaiu'e 
(>1 Jatei’ite in Western Australia'^ (1018, p. 800) he puts forvv'urd the g-eiieral 
eonelusion that ''c.iira, ordinary dijfrrrnrcs in laferite level in adjacent areas 
indicate block faal'tiny,'' citing- as evitlenee the iaterite-covered Ridge Hill 
Shell. These conclusions appear to he based on the supposition that the high- 
h^'cl laterite on the Darling Plateau which is exposed at an elevation of 
approximately 700 feet on Gooseberry Hill the east, of the Ridge Hill JShelf 
is the sani(‘ as the ^1(0*110 covering the Ridge Hill Shelf (at an elevation of 
apju*o.\imately ‘ibO feel). Xo dtfailed iinestigation of these laterites has pre- 
viously been made and i7i order to test Woolnough’s conclusions and to 
obtain turther infoi’ination about the vexed question of the origin of the 
low-level latei-ile and of' tlu' Darling Scarp a detailed survey of an area 
of a]))n'oximulelv tAVo S(|uare miles in the \icinity of Ridge Hill has beeji 
made by senior students of the De])artmcnt of Geology of the Univer’sity 
yl A\ csteru Ansti-alia working under tht^ author’s guidance. In the course 
ol this survey (mad(‘ iti ])art by plane table - telescopic alidade and in part 
by chain-compass-liarom(d(w methods) further study Avas made of the Pre- 
Camljriaii conijilox of the Darling RangCj a group of ])reviou,s]y unrecorded 
sedimentary I'ocks Avas dist-overed, the re]ationshi])s of the high- and low- 
level laterites were examiiu'd and an investigation into the origin of the ex- 
tensive sand areas fronting the Darling {Searj) was made. The present paper 
Sets out the r(‘sults ot‘ these iiiA'esligations. 
IT. PHYSIOGRAPPIY. 
The area examined is situated on the south side of the Helena valley 
adjacent to the Avestern boundary of the Darlington Area (Clarke and Wil- 
liams, 1920, iilate XXITI), It lies entirely on tlie Darling Scarp and ex- 
tends from tiic high-hn-el plateau, outliers of which occur iji the south- 
eastern coiaier of the area, almost to the Oat, low-lying country of the coastal 
])Iain to the A\est. It therefore co\ers the area i'e|iresent.ed on Woolnough’s 
generalised section (1020, p. 20) from the Darling Plateau to the Swan 
Coastal Plain in the same \A'ay as tlu' area mapped at Armadale { Prider, 
1941) covers a sojuewhat similar generalised section of tlie Scarp aiAproxi- 
mately lo miles lo the soutli of Ridge Hill AA’hich has been published bv 
Yb>olnough (1918, p. 391). 
The main eharacteristies of the Darling Scarp have been sufficiently 
described by ])revious authors (see for exnmjdo -Jutson, 1934, pp. 84-87) 
a?id re(inire no further consideration here, and attention Avill be conlined 
to the topogrni)hic featui'cs of the IDdge Hill area itself. 
The Draiiuifje Pattern . — The Scarp is dissected by: (a) the wsterly 
floAviiig streams, the Helena IHver and Parrants Creek, AA'hieh are conse- 
quent streams OAving their dcAmlopment to uplift of the Darling Plateau 
to the east: (b) minor streams iiowiug approximately parallel to the scarp 
AA'liieli have produced the dissected foothill zone mentioned by Wooluough 
(1929, ]). l'>). Such streams are Stathams Creek draining into the Helena 
to the X.X.E. and the tributary of lYirrants Creek draining to the S.S'.W. 
These appear to ho subsequent streams (Clarke, Prider and Teiehert, 1944, 
p. 78) Avliose direction has been determined by the X.N.E. strike of the 
sliear stnictiu’es in the granitic rocks and also by Hie presence of epi- 
