CVIII. IRRIGATION GEOLOGICALLY CONSIDERED. 
tributaries even as far west as Broken Hill and Mt. Poole. 
Some of these wells especially those near Broken Hill have 
already been described by Mr. W. Anderson.* 
The occurrence and the character of the water in this 
formation appears to be extremely capricious. Many wells 
fail to reach any supply of water at all, while of those 
which strike water one may yield fresh water while an 
adjoining well will yield brackish or salt water. The 
probable explanation of the latter phenomenon is that the 
water-bearing beds of sand or gravel in this formation are 
more or less irregularly distributed throughout the pre- 
valent mass of marls and clays, and are lenticular in 
character, so that in the case of two contiguous wells of 
about the same depths and surface levels it by no means 
follows that they derive their supplies of water from the 
same stratum. These wells are mostly shallow, the depth 
rarely exceeding 200 feet. In no case with which we are 
acquainted has the age of the strata in which these wells 
occur been proved to be as old as Tertiary. 
Il]. ARTestAN WATER IN AUSTRALIA.—(1) Perth Area, 
West Australia.—This area consists of a narrow coastal 
plain extending between the western fianks of the Darling 
Range and the Pacific Ocean. Its width at Perth is about 
15 miles, widening somewhat in a northerly direction. The 
greatest altitude of the intake beds where they dip off the 
flanks of the Darling Range must be some distance to the 
north of Perth, probably near the source of the Swan River, 
for the “‘rest point’’ of the artesian water at the Guilford 
Bore is at a greater altitude than the eastern edge of the: 
coastal plain where it meets the Darling Range near Guil- 
ford. The rock underlying the surface of this coastal plain 
is a coarse and very porous eolian sandstone, containing 
fragments of marine shells of existing species. Its disinteg- 
* Ann. Rept. Mines Depart., N. S. Wales, 1891, pp. 254 - 257. 
