42 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
are being produced. Take, for example, two of the most 
familar rocks to all of us—Coal and Chalk. To the east of us 
lie the great coalfields of Lancashire, to the N.W. the Chalk 
of Antrim, so both are our near neighbours, and our own 
Imestone at Castletown and Port St. Mary is only a harder 
and less pure form of chalk. We associate each of these common 
rocks, coal and chalk, with cone particular chemical element, 
coal with carbon, and chalk with calcium; and when the 
useful substances coal and chalk are used up, or disappear as 
such, the elements carbon and calcium are set free to reappear 
again later on somewhere else in nature in their beneficent 
scheme of world-wide circulation. Notice the periodic change. 
When we burn our coal we release the carbon from the condition 
~ in which it has been held or imprisoned since the Carboniferous | 
period, perhaps twenty million years ago. The carbon is given 
off in the form of noxious gases which are poisonous to man, and 
yet—paradoxical as it may seem—without which man and 
all other animals on this globe could not exist—without which 
life, as we now know it, would not be possible—as these gases 
supply the small amount, only three parts m 10,000 of carbon 
dioxide in the atmosphere, which 1s required as food by the 
green plants upon which all animals depend for their very 
existence. Our coal beds represent the forests and swamps of 
the Carboniferous age, and the heat and light given out by 
the coal as we burn it to-day may be referred to as the bottled- 
up sunshine of that far-back period by virtue of which the 
green plants then existing were able to appropriate and fix 
the carbon from the gases of their atmosphere. Nature, as it 
were, invested her capital in the plants of the Carboniferous 
period, sank it in fixed carbon, and man is now reaping the 
benefit and enjoying the unearned increment in the form of 
steam ships and railways, and all the modern manufactures 
that depend on coal. 
Carbon, then, in the history of the world, has been some- 
