A PIECE OF COAL. 
177 
the floor. When we land on the floor of the gallery 
we shall find ourselves in a kind of tunnel with railway 
lines laid along it and trucks laden with coal coming 
toward the cage to be drawn up, while empty ones 
are running back to be loaded where the miners are 
at work. Taking lamps in our hands and keeping 
out of the way of the trucks, we will first throw the 
FIG. 48. Imaginary section of a coal-mine. 
light on the roof, which is made of shale or hardened 
clay. We shall not have gone many yards before 
we see impressions of plants in the shale, like those in 
this specimen (Fig. 49), which was taken out of a coal- 
mine at Neath in Glamorganshire in England. You 
will recognise at once the marks of -ferns (a), for they 
look like those you gather in the hedges of an ordinary 
country lane, and that long striped branch (6) does not 
look unlike a reed, and indeed it is something of this 
kind, as we shall see by-and-by. You will find plenty 
of these impressions of plants as you go along the gal- 
