436 Proceedings of Boyal Society of Edinburgh, [jult 16 , 
3. On the Fossil Plants in the Ravenhead Collection in 
the Liverpool Museum. By R. Kidston, Esq. 
4. On the Action of Carbonic Acid Water on Olivine. By 
Alexander Johnstone, F.G.S., Assistant to the Professor of 
Geology., Edinburgh University. 
In a paper, entitled “ On the Action of Carbonic Acid Water on 
Minerals and Bocks,” read before the Edinburgh Geological Society 
on the 18th February 1886, and subsequently published in their 
Transactions for that year (vol. v. part ii. p. 282), I gave some 
account of the simple experiments made with a view to elucidate 
the action of carbonated water on various minerals, which up to 
that period I had been able to carry through. The minerals which 
I had at that time submitted to the action of carbonic acid water 
were the commonest rock-forming felspars, viz., ortho clase, oligoclase, 
and labradorite ; the micas, — muscovite and biotite ; black amphi- 
boles and pyroxenes, — hornblende and augite ; the anhydrous iron 
oxides, — magnetic and haematite ; and the rhombohedral carbonates, 
— cal cite and siderite. 
On a certain quantity of each of those mineral substances, I 
allowed a litre of distilled water, saturated with carbonic acid gas, 
and kept at a nearly constant equal temperature (about 4° C.), to act 
for a certain time. In some cases I permitted fresh air to come 
repeatedly into contact with the moist mineral, in other cases I 
carefully excluded atmospheric air. As the result of these experi- 
ments, I found that in nearly every instance the mineral which 
repeatedly encountered air plus carbonic acid water, changed and 
disintegrated far more rapidly than its neighbour which was care- 
fully protected from the atmospheric contact. I have since the 
beginning of the year 1886, continued, with occasional interrup- 
tions, my investigations into this important matter, and have found 
that almost every rock-forming mineral and rock which I have 
submitted to the action of the carbonated water, has become, in a 
comparatively short period, altered chemically and mechanically, 
and also in a greater or less degree disintegrated. I have paid 
