200 
Geology of Sydney. 
and noble rivers, fed in their turn by mountain tor- 
rents, and gradually stratified beds grew layer by layer 
above the coal. 
The amount of vegetable matter in a single coal- 
seam six inches thick is greater than the most 
luxuriant vegetation of the present day would furnish 
in 1,200 years. Boussingault calculates that luxuriant 
vegetation at the present day takes from the atmo- 
sphere about half a ton of carbon per acre annually, or 
fifty tons per acre in a century. Fifty tons of stone- 
coal spread evenly over an acre of surface would make 
a layer of less than one-third of an inch. But suppose 
it to be half an inch, then the time required for the 
accumulation of a seam of coal three feet thick — the 
thinnest which can be worked to advantage — would be 
7,200 years. If the aggregate thickness of all the 
seams of coal in any basin amounts to sixty feet, the 
time required for its accumulation would be 144,000 
years. 1 
A long time truly for our coal to form, and a 
vastly longer period until its energies came to be 
utilized by man. The late Professor Huxley wrote on 
this aspect of the question : — 
“ Nature is never in a hurry, and seems to have 
had always before her eyes the adage, * Keep a thing 
long enough, and you will find a use for it.’ She has 
kept her beds of coal many millions of years without 
being able to find much use for them ; she has sent 
them down beneath the sea, and the sea-beasts could 
1 WinciieU's Geological Sketches. 
