96 WATER SUPPLY IN THE INTERIOR OF NEW SOUTH WALES. 
centration which has been reached by the waters. A noticeable 
feature in the formation of the western plains is the wide distri- 
bution of gypsum in nodules and beds interstratified with the 
clay 
tanks and wells, and also on the surface in places ; and on ques- 
tioning well-sinkers, I was es struck by the generally expressed 
opinion that pinged ct ead gypsum you will find salt water 
not far off. e manner of formation of gypsum will show that 
the generalization akhod by the practical experience of the well- 
sinkers is Lae bly not far from the truth. 
Professor A. Geikie, LL.D., F.R.S., Director-General of the 
Geolo ayieal — of Great Britain and Treland, says—(Text-book 
of Geology, p. 398) :—‘‘ The study of the precipitations which take 
place on the floorsof modernsalt lakes is important, asthrowing light 
on the history of a number of chemically-formed rocks. The salts 2 
these waters accumulate until their point of saturation is reached, 0 
until by chemical re-actiontheyare thrown down. e least soluble 
sodium can begin to be deposited. Hence the concentration 
and evaporation of the water of a salt lake having a composition 
like that of sea-water would give rise first toa a layer or sole of 
A baa followed by one of rock-salt. This has been found to be 
the normal order among the various saliferous formations in the 
oatthi's crust. But gypsum may be precipitated without rock-salt, 
either because the water was diluted before the point of saturation 
for rock-salt was reached, or because the salt, if mt een was sub- 
sequently dissolved and re emoved.” Sir A. 0, Ram say, LL.D. 
F.R.S., P.G.S., President of a British Association for the 
Advancement of Science, has connected the occurrence of certain 
red formations with the existence of salt lakes, from the bitter 
waters of which not only iron of oxide, but often rock-salt, 
magnesian Sabon, and gypsum, were thrown down. He 
points to the presence of land plants, footprints of amphibia, and 
other indications of terrestrial surfaces, while truly marine organ- 
nt altogether. 
(Geikie, Text-book of Geology, p. 711) ; also (Inaugural Addréi to 
British Association for the Advancement of Science, 1880, by A.C. 
Ramsay, Presiden nt). The absence or scarcity of marine oF 
lacustrine fossils (for we cannot say they are absent) in the 
Darling te of recent deposit is not without a parallel in 
formations of a similar character now being deposited in other parts 
of the world. P vihoaine Geikie says :—“ As the level of the Dead 
