34 
formation in the tube before it was opened. Thus there can 
be no doubt that the greater part of the malachite formations 
have been produced by the action of water containing car- 
bonic acid gas in solution upon cuprous oxide, as the mala- 
chite of the Gumeschewskoi Mine, near Ekaterinenburg, in 
Russia, is found deposited in a dark-coloured clay which pene- 
trates a small limestone ridge, the whole formation finally 
resting upon chloritic slate, I have examined numerous 
specimens of malachite from all parts of the world, and have 
always observed strong evidence of the action of water upon 
them, there being numerous cavities always present, which 
exhibit deposits of cuprous oxide, or hydrated ferric oxide 
in their interiors, and occasionally amorphous silica and 
calcite. Gustav Rose (Mineralogische-geognostische Reise 
nach dem Ural, dem Altai und dem Kaspischen Meere ? 
1837), was of opinion after examining the copper formations 
in the Ural and Altai districts that the cuprite there was 
formed by direct oxydation of the metal; and, secondly, 
that the large malachite deposits were formed from the 
cuprite. This opinion probably well expresses the actual 
process which eventually resulted in the formation of mala- 
chite, as the presence of the clay surrounding the ore, the 
limestone formation and the hydrated ferric oxide and horn- 
stone (amorphous silica) shows that the former neighbouring 
crystalline rocks must have been submitted to the powerful 
action of water, which in all probability contained carbonic 
acid gas. Rose does not give (so far as I am aware) any ex- 
perimental proofs of his theory of the formation of the great 
copper deposits of the districts above mentioned. I con- 
sidered it therefore necessary to endeavour to determine 
experimentally the accuracy of his statement. For this 
purpose I placed perfectly clean polished strips of chemically- 
pure copper sheet in a glass tube, and covered them with 
distilled water saturated with carbonic acid gas; the tube 
was then sealed up and heated in a water-bath at 100° for 
