Vice-President’s Address. 287 
probably not greatly err in estimating the rate of formation 
of the clays and shales of the Upper Carboniferous Rocks if 
we set that rate at 1 foot in 3000 years. Now, the Upper 
Carboniferous Rocks of the South Wales Coal-field are said 
to be 14,000 feetin thickness. Of these, about half the thick- 
ness may be set down as sandstones, and the remainder of clays 
of one kind or another, together with coal-seams. Seven thou- 
sand feet of sandstone, if formed at the rate of 1 foot in 1500 
years, give us 10,500,000 years; while 7000 feet of clays, at 
1 foot in 3000 years, give an additional 21,000,000. To this 
we have to add the time required for the formation of the 
105 feet of coal, which is said to be the aggregate thickness 
found in the Upper Carboniferous Rocks around Manchester. 
In regard to these one may remark, it may be possible to 
“hurry up” in estimating the rate at which sandstones and 
a few other deposits have been formed, but when we are 
asked to do this in connection with either limestones or 
coals, the case appears to me to be very different. One has 
to remember that all vegetation derives its fixed carbon 
from the atmosphere alone, and that it does this under the 
combined influence of solar energy and its own vital force. 
The proportion of carbon-dioxide at present existing in the 
atmosphere is very small, ranging from an average of ‘04 / 
to a maximum of ‘10 /% A larger percentage than this 
latter is said to be detrimental, rather than conducive, to the 
growth of vegetable life. The supply of carbon-dioxide, 
which balances the demand made by the formation of 
limestones (in every cubic foot of which 16,000 cubic feet 
of carbon-dioxide are locked up) and of coals (of which 
carbon constitutes from 60 to 90 /), is met partly by the 
products of animal respiration, partly by the products of 
the decomposition of organisms, both vegetable and animal, 
but mainly from exhalations from volcanic sources. In the 
formation of eruptive rocks, a large quantity of carbonates 
of lime and other bases must be constantly passing back 
into their initial stage, that of combination in the various 
silicates. In this process carbon-dioxide is now, as it 
must always have been, liberated in considerable volumes. 
Bischoff estimates that 1,855,000,000 cubic feet of this 
