A PIECE OF COAL. 
plant, puzzled those who found it for a very long time. 
At last, however, Mr. Binney found the specimen 
growing to the bottom of the trunk of one of the fossil 
trees with spotted stems, called Sigillaria; and' so 
proved that this curious pitted stone is a piece of fossil 
root, or rather underground stem, like that which we 
found in the primrose, and that the little pits or 
dents in it are scars where the rootlets once were 
given off. 
Whole masses of these root-stems, with ribbon-like 
roots lying scattered near them, are found buried in 
the layer of clay called the underclay which makes the 
floor of the coal, and they prove to us that this under- 
clay must have been once the ground in which the 
roots of the coal-plants grew. You will feel still more 
sure of this when you find that there is not only one 
straight gallery of coal, but that galleries branch out 
right and left, and that everywhere you find the coal 
lying like a sandwich between the floor and the ro.of, 
showing that, quite a large piece of country must be 
covered by these remains of plants all rooted in the 
underclay. 
But how about the coal itself? It seems likely, 
when we find roots below and leaves and stems above, 
that the middle is made of plants, but can we prove 
it? We shall see presently that it has been so crushed 
and altered by being buried deep in the ground that 
the traces of leaves have almost been destroyed, though 
people who are used to examining with the miscro- 
scope, can see the crushed remains of plants in thin 
slices of coal. 
But fortunately for us, perfect .pieces of plants have 
