12 The Formation of Gold Nuggets. 
posed, influencing the precipitation of the gold, which 
concreted, so to speak, around the most congenial nuclei 
presented to it, such as the particles or pieces of reef gold 
existing in the drifts or any other metallic substances for 
which it had an affinity. 
Mr. Daintree, formerly of our Geological Survey, had on — 
one occasion prepared for photographic uses a solution of 
chloride of gold, leaving in it a small piece of metallic gold 
undissolved. Accidently some extraneouus substance, sup- 
posed to be a piece of cork, had fallen into the solution, 
decomposing it, and causing the gold to precipitate, which 
deposited in the metallic state, as in the electro-plating 
process, around the small piece of undissolved gold, increasing 
it in size to two or three times its original dimensions. 
Considering this accidental experiment of Mr. Daintree as 
in some measure bearing out Mr. Selwyn’s hypothesis, 
I was induced to make a few simple experiments, the 
results of which I have now the pleasure of laying before 
you. 
Using the most convenient salt of gold, the terchloride, 
and employing wood as the decomposing agent, in order to 
imitate as closely as possible the organic matter supposed to 
decompose the solution circulating through the drifts, I first 
immersed a piece of cubic iron pyrites taken from the coal 
formation at Cape Otway, far distant from any of our gold 
rocks, and therefore less likely to contain gold than other 
pyrites. This specimen (No. 1) was keptin a dilute solution © 
for about three weeks, and is completely covered with a 
bright film of metallic gold. I afterwards filed off the gold. 
from one side of a cube crystal to show the pyrites itself 
and the thickness of the surrounding coating, which you 
will observe is thicker than ordinary note paper. If the 
conditions continued favourable for a very lengthened 
period, this specimen would doubtless have formed the 
nucleus of a large nugget. Crystals of gold have been 
found to contain nuclei of brown iron ore and undecomposed 
iron pyrites. 
No. 2 specimen contains iron pyrites, and was immersed 
in a solution of about 4 grs. of the chloride of gold to one 
ounce of water ; ina short time, however, it was found that 
in such a strong solution the pyrites began to decompose ; 
but after diluting to about 2 ers. to an ounce of water this 
decomposition apparently ceased, and metallic gold deposited 
wherever a particle of the sulphide existed, alike in crevices 
