246 
C. E. S. Davis. 
In tli(* (‘astorri part of the eountry shown on the locality ])lan, the main rock 
type is ^’ranitic, covered in the higher country by a ca[>ping of laterite. 
The granite is cut by quartz masses (mainly thin veins^ but there is also a 
huge (jiuutz blow at Gosiiells) and by basic dykes. On the western margin 
of the granite, stee))ly-dipping, slightly metamorphosed Pre-Cambrian 
sediments of tlu* Cardup Series outcrop from (Josnells intermittently south- 
wards. 
The Cardup Series and granitic, rocks close to the contact at Armadale 
were studied in l!)30 (Prider, 1941), and, in 1940, areas were map])ed at 
Gosnells and at Wougong-Chirdu]), respis-tively north and south of Armadale. 
At the end of the description of the Wongong-Cardui> area (Thomson, 1941) 
the knowledgt' gaimal and the problems arising from the study of aU three 
areas have Ixarn summarised. 
The (lOsnells Area is a strip of th(‘ scarj) about 4 miles long ami 1% 
miles wide. Particular altention was i)aid to the northern part where the 
Cardup Series and quartz blow crop out, and the granite, basic dykes and 
quartz are exposed in (piarries. The coiiidiy was map])ed entirely by pace- 
and compass-traversing by the writer working alone. These traverses were 
tied ire(|uently to th(» Lands and Survey l)<q>artment’s pegs. .Form lines 
were dravm from levels obtained by aneroid baromCer leadings, woi'king 
from Gosnells railwav station as datum. 
IT. PHVSIOGPAPHY. 
A. (reneral Features. 
East of the i)resent foot of the Darling Scarp, there was originally a 
laterite-covered iiemqilain (Jutson, 1934, p. 291). This ))eneplain was later 
elevated and youtld’ul, westerly-tlowiiig streams have now remo\ed the 
laterite and ex]>osed tlu' underlying pre-Cambrian rocks along a belt, gener- 
ally from hall a mile to two miles wide. Pre-Ckimbrian rocks are exposed 
fartlier east, only in the valleys of the larger streams and in some moiuuhiocks 
rising above the plateau. 
B. The Barling Scarp. 
As Jutson concludes (1934, p. 87), the elevation of the Darling peiu'plain 
was effected by faulting, but the present face of the Darling Scarp is to the 
east of the actual fault-plane. Ko trace of the fault Avas detect(‘d in the 
Gosnells area. 
W oolnough (1918, ]>. .399) believes tltere were two periods of uplift 
of the penei)lain. After tin* first movements, mature valleys Avere formed 
which now occu|)y so much of the inland “wheat-belt’^ country: and later 
movemmds elevated the ])ene[)lain io its present height. 
The topography of parts of the Gosnells area is comi)osite, and supports 
Wooluough’s belief. This is especially marked in the valley of Ellis Brook, 
which is mature above a height of 929 feet (the lop of the Rixty Foot Falls). 
At and just l)elow the falls, the streuTU bed <lrops over 190 feet and the sides 
of the A'alley stee]>en considei'ably. Fpstream are some meanders, now slightly 
entrenched. In many other ]daees, the scarj) (lattens a])ove a height of about 
500 feet. Clarke and AVilliams (1929, p. 167) note that terraces at a height 
of 450 feet in the Helena valley probably record a pause in ui)lift along the 
Darling fault. 
