NOTE ON THE ORIGIN OF MALACHITE, 419 
the descent of waters from the surface charged with carbonic acid 
and carbonate of lime, will change the sulphate crystals into 
malachite ; and that this alteration will proceed without change 
of form is highly probable. That this has been the mode of for- 
mation of the fibrous malachite in the cupriferous schists of 
Girilambone the writer has no doubt whatever, and he believes 
that the explanation will hold good for all occurrences of the 
mineral. 
The following is suggested as the series of changes which have 
produced the carbonates of copper :— 
I. A period of wet weather during which the rocks and ore 
formations within surface influences become saturated with, and 
all cavities full of, water. 
II. A period of dry weather. At first the excess of water 
drains off rapidly, leaving the rocks merely wet all through. As 
the drying proceeds oxidation of the damp minerals goes on very 
fast and sulphates are formed. The flow of water is insuflicient 
to carry these far, so they saturate part of the adjacent earthy 
minerals, and also effloresce in cavities, particularly where there 
is a current of air. Finally at the end of the dry period the sul- 
phates will be left as such, forming quite dry mixtures with other 
substances, and incrustations or crystals in cavities and fissures. 
{II. Another wet period arrives. At first the descending 
water permeates slowly and is saturated with carbonic acid and 
soluble carbonates, the slow soaking of which over the dry sulphates 
converts the latter into carbonates. As the volume of water 
increases, the CO, and soluble carbonates become less, but the 
sulphates will have been already converted into carbonates, so 
they are not dissolved. Finally the rocks become saturated with 
water, the wet period passes away, and another cycle of change 
‘commences. 
Every cycle will add fresh layers of carbonate to the incrusta- 
tions, and fresh crystals to the fibrous bundles in the cavities, 
Until at last solid masses of concretionary and fibrous crystalline 
malachite result. 7 
