iant growth of vegetation,
combined with the other necessary conditions, has ever existed at any
other period in the history of the globe. Thus in the very oldest rocks of
Canada and the northern States of America, in strata which take us back to
the dawn of geological history, there is found abundance of the mineral
graphite, the substance from which black-lead pencils are made, which is
almost pure carbon. Now most geologists admit that graphite represents the
carbon which formed part of the woody tissue of plants that lived during
those remote times, so that this mineral represents coal in the ultimate
stage of carbonization. In some few instances true coal has been found
converted into graphite _in situ_ by the intrusion of veins of volcanic
rock (basalt), so that the connection between the two minerals is more
than a mere matter of surmise.

Then again we have coal of pre-Carboniferous age in the Old Red Sandstone
of Scotland, this being of course younger in point of time than the
graphite of the Archaean rocks. Coal of post-Carboniferous date is found in
beds of Permian age in Bavaria, of Triassic age in Germany, in the
Inferior Oolite of Yorkshire belonging to the Jurassic period, and in the
Lower Cretaceous deposits of north-western Germany. Coming down to more
recent geological periods, we have a coal seam of over thirty feet in
thickness in the northern Tyrol of Eocene age; we have brown coal deposits
of Oligocene age in Belgium and Austria, and, most remarkable of all, coal
has been found of Miocene, that is, mid-Tertiary age, in the Arctic
regions of Greenland within a few degrees of the North Pole. Thus the
formation of coal appears to have been going on in one area or another
ever since vegetable life appeared on the globe, and in the peat bogs,
delta jungles, and mangrove swamps of the present time we may be said to
have the deposition of potential coal deposits for future ages now going
on.

Although in some parts of the world coal seams of pre-Carboniferous age
often reach the dignity of workable thickness, the coal worked in this
country is entirely of Carboniferous date. After the explanation of the
mode of formation of coal which has been given, the phenomena presented by
a section through any of our coal measures will be readily intelligible
(see Fig. 1). We find seams of coal separated by beds of sandstone,
limestone, or shale representing the encroachment of the sea and the
deposition of marine o