The Geology of the Darling Scarp at Ridge Hill. 
Ill 
(1) The ferraginoits sandstone -series t'orms a thin cover on tlie Ridge 
Hill Shelf where it lies unconformably on highly kaoliiiised granites. The 
unconformity is an undulating surface (see text hg. 2). The eastern contact 
of this series with the granite trends in a northeasterly direction and thus 
bears no relation to the supposed Darling Fault which trends due north. 
In the north-west part of the area small streams have cut down through 
this series to expose the underlying Pi'e-Cambrian rocks to the west of the 
ferruginous sandstone outcrops. 
Text fig. 2. — H.W.-X.E. section of South side of Helena Valley from the Helena 
\'alley to the Ridge Hill shelf showing unconformity between the ferrii- 
giiKJus 5-aiulstone scries (sandstone underlain by conglomerate and overlain 
by low level latei'ite) and the Pro-Cambrian (granite and epidiorite) . 
The series consists mainly of feiruginous sandstones underlain in ])laces 
by I)oulder conglomerates. Outcroj)s of tlie boulder conglomerates occur 
at (iO chains N. 10° P]. and (>7 chaijis N. 5° W. from Ridge Hill Siding. The 
slopes below the outcrop of ferruginous sandstom* in the northern part of 
the ar(‘a are strewn with well-rounded waterworn boulders which appear to 
have becii derived from this conglomerate. These bouldei's ha\e not been 
found in other parts of the area suggesting that the conglomerates are con- 
fined to that part of the ferruginous sandstones clost'sl to the ))i'(‘seni, Helena 
Ri\(*r. Since the known outcrops of conglomerate arc at lev'els below the 
sandstones and are confined to the small area lying to the south of the Helena 
River it a]^pears that they form a localised basal layer in the sandstones 
probably indicating an old stream channel or narroAV embayment in tlie 
coast. It is interesting to note that Fletcher and Hobsim (19;12) have 
described a similar occurrence of feiTuginous sandstone with rounde<l (|uai’iz 
I'ebbles nnderlying a low-level laterite in the Savuii Valley at Uiiper Swan. 
This deposit they refer to as the ^^Older Alluvium”. It occurs at an elevation 
of from 250 to 300 feet (the same as the Ridge Hill ferruginous sandstones). 
(i) The conglomerates at Ridge Hill consist mainly of hfiuldcrs and 
cobbles of granite, epidiorite and (piartz, up to 18 inches diameter. All 
are stronolv rounded and one water-worn granite boulder collected from 
a spot 05 chains N. 10° E. from Kidge Hill siding is a perfect ellipsoid 
of n'volution with major diameter 11 inches and minor diameter five 
inches. This has the appearance of a beaeh l)onlder but it is doubtful 
whether such shape is indisputable proof of beach action (Wentworth, 
