E. F. PITTMAN AND T. W. E. DAVID. CIX. 
ration has resulted in the formation of a surface covering 
of sand. So faras is known, the underlying strata pene- 
trated by the bores consist of sandy shales and clays. But 
it appears that no continuous bed of impermeable material 
exists. It has been observed by one of us (KE. F. Pittman) 
that after heavy rain on the Darling Ranges strongly 
flowing streams coming from the Ranges when they reach 
the coastal plain are very quickly absorbed by the porous 
rock. The deepest of these wells was about 1,800 feet, 
and the yield varies from 69,120 gallons per diem to 1,120,000 
gallons per diem. The temperature of the water varies 
from 75° to 91° Fahr. The water contains from 30 to 90 
‘grains of mineral matter, (chiefly chloride of sodium) per 
gallon. Therock composing Rottnest Island, 12 miles west 
of the coast, opposite Perth, is of the same eolian character 
as that of the coastal plain. There must therefore be a 
leakage of the artesian water into the sea. 
A feature of special interest in this artesian basin is the 
apparent fact that there is an absence of any continuous 
impervious rock covering above the artesian water-bearing 
beds. . This suggests the inference that after all an imper- 
vious stratum is not an absolutely essential part of the 
structure of an artesian area. The only requisites of an 
artesian basin may be therefore defined as those of inclined 
deposits of porous rock resting on an impermeable floor, 
outcropping ata level higher than that of the site of the 
bore. From the observations of the West Australian 
engineers it has been ascertained that 96% of the total 
rainfall on the catchment of the Canning River and 98% in 
the case of the Helena River, is lost through absorption by 
the decomposed granite of the Darling Range. The water 
so absorbed presumably goes to feed the artesian supply. 
(2) The Collie Coal-field is a small isoiated artesian area 
at the southern end of the Darling Range. The artesian 
