364 H. P. Woodward — Dry LaJces of W. Australia. 



these, are areas of depression, in which the surface is for the most 

 part covered with sand, loam, or clay ; whilst from these valleys 

 rise steep rocky ridges consisting of hornblendic schists, dioi'ite 

 dykes, and quartz reefs, which compose the auriferous series. 



These valleys form the main drainage of the country, which falls 

 in a south-easterly direction, but so gradually, that the rain- 

 water, instead of cutting out a channel, spreads out in a broad 

 sheet over the flat surface, thus forming, during a wet season, 

 a series of large but extremely shallow lakes. 



The water shed from the adjoining hills naturally, in rushing down 

 their sides, carries with it not only such soluble salts with which 

 it comes in contact, but also a certain amount of clayey matter, 

 which is spread out in a thin layer over the plain, whilst the salts 

 held in solution are deposited as the water evaporates, the result 

 being the formation of numerous large salt clay-pans which have 

 incorrectly been called lakes. These clay-pans, for the most 

 part, run in chains, and are connected by channels — the whole 

 being fringed by blown sandbanks containing a large quantity 

 of gypsum, and upon which nothing but salt herbage, such as 

 salt-bush, samphire, and mesembryanthemums, will grow. The 

 beds of these pans are for the most part composed of a thin layer 

 of clay, which rests directly upon the upturned edges of the 

 highly inclined decomposed schists beneath. In other cases, the 

 covering of clay is entirely wanting, the floor being apparently 

 formed directly by the planed-down edges of the indurated rock, 

 which is often strewn with fragments of quartz, whilst here and 

 there huge reefs of this mineral outcrop at the surface. 



When these lakes occur in hilly country, they generally cover the 

 entire valley ; but when on the open plain, they are fringed by aeolian 

 deposits, which often resemble coastal sand-dunes ; whilst in other 

 cases, where hills occur upon one side, the rocks of which ai-e of a 

 highly decomposed nature, these latter are found to be eroded in such 

 a way that they form nearly vertical clifi's. Again, in the northern 

 portion of the field, where these lakes are met with in tracts of 

 country, the surface of which is covered by a deposit of indurated 

 ferruginous clay (cement), they are surrounded by nearly vertical 

 cliffs of kaolinized schists, capped by the above-mentioned recent 

 deposits. In this class of country also, branches of these flats run 

 ofi' from the main valley, which gradually split up into canyon-like 

 watercourses called " wash-aways." Immediately after heavy rain 

 is the only time that the surfaces of the lakes may be seen covered 

 by a few inches of salt water ; and, in rare cases, even by a few feet 

 when some obstruction to its flow has occurred. It must, howevei', be 

 borne in mind that these remarks do not refer to the small fresh- 

 water swamps and clay-pans, always spoken of as lakes, but to 

 those large areas which are marked upon the plans as such. 



As before stated, there is not sufficient slope in the surface of 

 the country or a large enough rainfall to form rivers ; also the 

 surface-area exposed to evaporation is too great to allow any of 

 the water to flow away ; therefore, not only is there a thin layer of 



