SALTER — A CHRISTMAS LECTURE ON COAL. 
237 
hollow space left beneath these gave rise to the original figure of the 
dome-shape of Stigmaria, and the idea of its being a floating plant, an 
idea which has fif^nred in a hundred essays on coal. It is an excellent 
proof how much our logic may go astray with the premises wrong. 
Lastly, as a conclusive proof of the marine nature of coal, the presence 
of very salt sea- water in it, containing iodine and bromine, might have 
been, and should have been, adduced. 
In p. 13, the printers or I have called paper coal " dysoile", instead 
of dysodile. 
In p. 183, I am made to say that plants give out less carbonic 
acid at night than they take in (by day) , The words in brackets 
should not be left out. 
But if I attempted to fill up all my own omissions I should fill this 
number. 'The greatest fault of all is to have talked in p. 13 of finishing 
in the next number or so, and then extend over half the year. 
A subject of such vital national importance ; a trafl&c which employs 
directly half a milHon of our countr}Tnen ; and whose yearly value, 
as raw or manufactured material, represents such enormous capital, 
cannot be a subject of indifference to any man. 
The question whether we can afford to go on digging away at the 
present rate, or even a greater one, and exporting to other nations as 
well as keeping up our own steam, has been already answered by my 
friend, Mr. Hull, in his excellent little book, " The Coal-Fields of 
Great Britain."* His results are summed up in the last page, and 
may be briefly given. 
" 1. There is coal, at various depths, over much larger areas than 
our maps give, down to depths of nine thousand or ten thousand feet, 
of which we are never likely to reach more than four thousand feet, 
from increase of temperature. 
" 2. There is a supply of coal within the smaller limit enough to 
afford sixty million tons a year for ten centuries." 
When our coal-fields are being exhausted, then the grand untouched 
deposits of America will come into play. Let us get out all we can ; 
distribute it as widely as the arts of peace require ; use it as care- 
fully as such a blessing should be used, and do all the good with it 
we may. 
1861 ! Stamford, Charing Cross. A new edition is in the press. 
