128 
Rex T . Pkideii 
The Hti’uclui'o ol‘ llu; IJai'ling Si'ai‘|) and Coastal Plain based on the 
assumption that the ferruginous sandstone series is of Lower Cretaceous age 
is shown diagrammatically in text fig. 7. 
Text fig. 7 . — Diagranunatic section (not to scale) of the Coastal Plain artesian 
basin on tlic assumption that the Kidge Hill ferruginous sandstones are of 
l.ower Cretaceous age (coinparal)le with the TUdlsbrook sandstones). 
(b) Tlir Darling Scarp . — Previous authors have considered that the 
‘‘fault’’ hy])otliesis tor the origin of the Darling Scarp is supported by 
evidence of shear structures in the Pre-Cambrian rocks (Saint-Smitli, 1912, 
p. 7] ; Hlatchford, 1912, p. 59) and l)y the high and low- level laterites which 
were considered to be an indication of blocdc faulting (AYoolnough, 1920, 
p. Ki). The main conclusions drawn from the evidence set down in tliis 
paper ai'e: — 
(i) There are no striu-tnres in the Pre-Cambrian rocks which can be 
related to the supposed Darling Fault. The shear structures are considtu'ed 
to be of late Archaeozoic age sinee some of them liave been replaced by 
quartz vdns which are iidrudcd by late Pre-Cambrian epidiorites, and hence 
much older than the ]iostulated Darling Fault. ^Moreover they deviate 
very considerably from the dij'ectioii of the Darling Scarj). 
(ii) The high- and low-level laterites were formed at different periods 
and are no indication of block faulting and therefore yield no evidence in 
favour of the Darling Fault hy])othosis, 
(iii) It has l)eeu shown that lU) fault exists between the eastern and 
western edges of the area mapped and therefore if the Darling Fault 
exists it must be situated some distance to the west of the Ridge Hill 
.Area, where it is covered by the yellow smuls. 
If these conclusions are valid there no positive evidence for the 
existence of the Darling Fault. Aloreover all the observed characteristics 
of the scarp are explicable by dilterential erosion of the hard Pre- 
Cambrian rocks to the east and the softer later rocks to the Avest of the 
scarp. 
V. ACKXOWl.FDCAIEXTS. 
The held survey work in Ihe Ridge Hill Area Avas done by various 
parties of senior students of the University Geology Department Avorkiiig 
under my supervision and their assistance is gratefully acknowledged. 1 
am indebted also lo Professor E. do C, Clarke for assistance during the 
revision of the text. 
