al basins of
Scotland and Ireland, of France and Belgium? And if these, why not those
of America and other parts? The deposition of the coal, according to the
theory here advanced, may as well have been brought about in a series of
large inland seas and lakes, as by one large comprehensive sea, and
probably the former is the more satisfactory explanation of the two. But
the astonishing part of it is that the changes in the level of the land
must have been taking place simultaneously over these large areas,
although, of course, while one quarter may have been depressed beneath
the sea, another may have been raised above it.

In connection with the question of the contour of the land during the
existence of the large lakes or inland seas, Professor Hull has prepared,
in his series of maps illustrative of the Palaeo-Geography of the British
Islands, a map showing on incontestible grounds the existence during the
coal-ages of a great central barrier or ridge of high land stretching
across from Anglesea, south of Flint, Staffordshire, and Shropshire
coal-fields, to the eastern coast of Norfolk. He regards the British
coal-measures as having been laid down in two, or at most three, areas of
deposition--one south of this ridge, the remainder to the north of it. In
regard to the extent of the former deposits of coal in Ireland, there is
every probability that the sister island was just as favourably treated
in this respect as Great Britain. Most unfortunately, Ireland has since
suffered extreme denudation, notably from the great convulsions of nature
at the close of the very period of their deposition, as well as in more
recent times, resulting in the removal of nearly all the valuable upper
carboniferous beds, and leaving only the few unimportant
coal-beds to which reference has been made.

[Illustration: FIG. 23.--_Cyathophyllum_. Coral in encrinital limestone.]

We are unable to believe in the continuity of our coal-beds with those of
America, for the great source of sediment in those times was a continent
situated on the site of the Atlantic Ocean, and it is owing to this
extensive continent that the forms of _flora_ found in the coal-beds in
each country bear so close a resemblance to one another, and also that
the encrinital limestone which was formed in the purer depths of the
ocean on the east, became mixed with silt, and formed masses of shaly
impure limestone in the south-western parts of Ireland.

It must be noted