Relations of the Atmosphere. 851 
kaolin 500 meters in thickness over the whole surface of the 
globe, would thus require an amount of carbonic dioxide 
equal to more than twenty-one times the entire weight of our 
present atmosphere. 
The absorption of this gas in the decay of silicates like 
hornblende, pyroxene and olivine is far greater. If we assume 
for convenience a hornblende containing 20:0 per cent of mag- 
nesia, and 14:0 of lime, with a density of 8-0 (which figtres 
are not above the average) we find that it will require 33-0 
per cent, or in round numbers one-third its weight of carbonic 
dioxide to convert these two bases into neutral carbonates; so 
that a meter-cube of hornblende, weighing 3000 kilograms, 
absorb 10,333 kilograms, or a whole atmosphere of this gas, 
being five times as much as is taken up in the kaolinization of 
the same volume of orthoclase. 
n this connection we revert to a farther calculation by Ebel- 
men, who pointed out that the conversion of 21,357 kilograms 
of ferrous oxide into 23,750 kilograms of ferric oxide would 
1m our atmosphere. 
belmen, at the same time, referred to the well-known 
deoxidation of carbonic dioxide by growing vegetation, and 
also to the reduction, by decaying organic matters, of sulphates 
to sulphids, with reproduction of carbonic dioxide, through 
Which the generation of metallic sulphids in nature gives to 
the atmosphere, in union with carbon, a portion of the oxygen 
previously combined with sulphur and with the metals. 
The following calculations may serve to bring still more 
fully before us the great geological significance of these atmos- 
heric changes. The weight of a layer of pure carbon, with a 
density of 1°25 and a thickness of 0-7 meter, would require for 
its Conversion into carbonic dioxide the whole of the oxygen 
of our present atmosphere. The separation of such an amount 
