GOLD AT MOUNT MORGAN. 
210 
the decomposition of chlorides with manganese, which occurs 
sparingly in the form of pyrolnsite along with the ironstone 
of Mount Morgan.” 
In Mr. Jack’s opinion, the great geyser which has built up 
Mount Morgan was of Tertiary age, and broke through the 
sandstone, which has been traced over a very large area in 
Northern Queensland, and was named by the late Mr. 
Daintree the Desert Sandstone, and believed to be post 
cretaceous. In many places the valleys eroded out of this 
sandstone became the seats of volcanic action, the volcanoes 
breaking out in the upper parts of the valleys and filling the 
lower reaches with floods of basaltic lavas. The geyser 
would thus probably be contemporaneous, or nearly so, with 
the basalts, which have been the causes of the wealth of 
Victoria, by covering and so protecting from denudation so 
much of the old auriferous gravels. 
The main deposit of gold is in the central core and the 
summit cap of the hill, probably the solid filling of the pipe 
and basin of the geyser ; the siliceous sinter being much 
less rich, and some aluminous deposits, apparently similar to 
those of some of the mud volcanoes of the Yellowstone, being 
quite free from the precious metal. 
The solution and deposition of gold in the manner here 
supposed is of very great theoretical interest. Given a 
chlorinated water, the solution of gold from previously 
existing reefs is of course easy, but since these, without 
doubt, owed their origin to the deposition of gold from the 
water which also deposited the quartz, we are not shut up to 
the explanation, and may, if we please, take it as only a 
special case of deposition from deep-seated springs. 
The late J. A. Phillips described some years ago the 
numerous metallic deposits from a modern hot spring in 
California, and the very wide distribution of gold, though of 
course in very small quantities, has long been known. It has 
been proved to exist in sea water. Plates of copper exposed 
on a ship’s side through a considerable length of time had 
gathered quite recognisable traces, and the processes of 
deposition from solution have been studied by Dr. Skey, of 
New Zealand, and the researches published in the “Chemical 
News” for 1874, Vol. XXX., pp. 151, 171. 
In the character and distribution of the gold Mount 
Morgan is again extraordinary. It is the only known gold 
which is free from silver, and is also the purest known, as it 
assays up to 99*8 per cent., the part of impurity being 
copper, with a trace of iron. It is a curious circumstance 
that in Australia, with few exceptions, the purity of the gold 
