Vice-President’s Address. 289 
of a foot of coal may be has been variously estimated—no 
two persons agreeing even approximately. Professor Huxley 
(“Formation of Coal,” Contemporary Review, 1870, p. 627) 
suggests a possibility of it being about 1 foot in 500 years. 
Boussingault estimates (Smithsonian Report for 1857, p. 188) 
that luxuriant vegetation at the present day takes from 
the atmosphere about half a ton of carbon per acre annually, 
or 50 tons carbon in 100 years. Fifty tons of carbon of 
the specific gravity of coal (about 1:5) spread over an acre 
would make a layer about + inch (1 inch in 300 years, 1 foot 
in 3600 years). Professor Phillips “ Life on the Earth,” 
p. 133, calculating from the amount of carbon taken from the 
atmosphere, as determined by Liebig, considers that if it 
were converted into coal, with about 75 pA of carbon, it 
would yield 1 inch in 127°5 years, or 1 foot in 1550 years, 
Humboldt’s estimate is 1 foot in 1800 years. Croll estimates 
it at 1 foot in 1600 years. 
These figures are given on the assumption that coal is 
a purely subaerial deposit. In studying the mode of 
occurrence of coal-seams in the field, I have, however, come 
to the conclusion that a fairly large percentage of coal-seams 
of Lower Carboniferous age represent the mean term of 
a series of rocks which have marine shale at one end and 
marine limestone at the other. I should infer from these 
facts that the rate of formation of the coals in question 
was intermediate in age as the seams are intermediate in 
geological position—between that of finely laminated marine 
clays on the one hand and marine limestones on the other. 
These Lower Carboniferous coals of submarine origin are 
marvellously persistent in both lthological character and 
geographical extent, and I fail to see any reason why they 
should not be fair representatives of the great majority of 
coal-seams of all other ages. 
Whether many will agree with me or not in these con- 
clusions is not very material, but the facts as they appear to 
me warrant us in assuming that the rate of growth of coal- 
seams went on at the rate of somewhere between 1 foot in 
3000 years and 1 foot in 6000. If we take the rate at 
the lower of the two estimates, 105 feet of coal, which is 
