1 86 THE FAIRY-LAND OF SCIENCE. 
remains would be preserved like those which we find 
now in the roof of the coal-galleries. 
But still there are the thick sandstones in the coal- 
mine to be explained. How did they come there ? 
To explain them, we must suppose that the ground 
went on sinking till the sea covered the whole place 
where once the swamp had been, and then sea-sand 
would be thrown down over the clay and gradually 
pressed down by the weight of new sand above, till it 
formed solid sandstone and our coal-bed became 
buried deeper and deeper in the earth. 
At last, after long ages, when the thick mass of 
sandstones above the bed b (Fig. 46, p. 174) had been 
laid down, the sinking must have stopped and the land 
have risen a little, so that the sea was driven back ; 
and then the rivers would bring down earth again and 
make another clay-bed. Then a new forest would 
spring up, the ferns, Calamites, Lepidodendrons, and 
Sigillarias would gradually form another jungle, and 
many hundreds of feet above the buried coal-bed b, a 
second bed of peat and vegetable matter would begin 
to accumulate to form the coal-bed a. 
Such is the history of how the coal which we now 
dig out of the depths of the earth once grew as beautiful 
plants on the surface. We cannot tell exactly all the 
ground over which these forests grew in England, 
because some of the coal they made has been carried 
away since by rivers and cut down by the waves of 
the sea, but we can say that wherever there is coal 
now, there they must have been. 
Try and picture to yourselves that on the east coast 
