Ci^ARKE . — Natural Itcf/ioias in IVcstern Australia. 
121 
gTowtli and consequently the country has not been settled to the 
same extent as the Jam country or the Salmon Gum country farther 
east’' (Gardner, A^ol. VII, p. 40). Tlie extent of this region, shown 
on the accompanying maj) (PI. XV), is greater than that of the 
AVheat Belt on the Agricultural Department’s map (Sutton), or in 
ilcLintock’s ‘-'Swan Geography” (p. 110), but there seems no rea- 
son, having consideration for annual rainfall, time of incidence of 
rain, and regularity, for regarding the eastern l)oundary of profit- 
able wheat-growing as coming mucli sliort of the 10" isohyet. 
A serious drawback shared by several regions to be later descril)- 
ed is the saltness of the ground-water and the absence of any 
artesian suj)ply. The supply of Avater is therefore entirely that 
which is held by STirface storage — natural or artificial. 
3. The Jarrah Region. This region has been geologically 
mapped only in small jnitches. It appears to consist essentially of 
metamorphic rocks (gneisses, etc-) seamed with basic dykes, the 
complex being thought to be of Pre-Cambrian age. The higher 
ground is nearly everyAvliere cai)ped witli latei'ite. Lateritic deposits, 
indeed, occur in many other parts of the State, but they are most 
extensively developed in the Jarrah Region. The soil formed by 
the Aveathering of the basic rocks is the most fertile. Over incoherent 
laterite the soil is slightly better thaii that derived from the more 
acid rocks, but Avhere, as is usually the case, the laterite is cemented 
into a ” cuirass”; it bars the doAvnward growth of the roots of most 
cultivated plants and consequently laterite country is generally un- 
suited for cultiA^atioii. It is, hoAvever, on the laterite that the Jarrah 
{Eucalyptus marginata) grows best (Gardner, 192.‘b2o, Vol. VI, p. 
104). The region is named after its most important product, but 
includes more than the “prime” Jari-ah area (see Gardner, o]). cit.). 
ComparatiA^ely small areas of down-faulted Permo-Carboniferous 
sediments carrying coal seams occur at Collie and at Wilga (a fcAV 
miles south of Collie), and are of economic ini))ortance (Maitland, 
1919, (a), p. :18, 1919, (b), p. 3)- 
The Avestern part of this region is the <lissected Avestern margin 
of the Great Plateau of Western Australia (Jutson, 1914, p. 19) 
hounded on the Avest by the Darling Fault. The topography near 
the fault-line scarp is somewhat rugged, passing in a distance of d 
miles or so to the east into the more gently unduhiting contours of 
the eastern ]>art of the region, Avliich in turn merge into the still 
more monotonous landscape of the Wlieat Belt. This region has 
a rainfall, predominantly Avinter and remarkably regular, of be- 
tAveen 25 and 40 inches per annum. 
