Yellow and gray sandstones, blue and black clays and shales,
bands of coal and ironstone, fossil plants, bivalves
and fish, occasional marine bands.

MIDDLE CARBONIFEROUS.
_Gannister beds_ or _Lower coal-measures._
_Millstone grit._ Flagstone series in Ireland.
_Yoredale beds._ Upper shale series of Ireland.

LOWER CARBONIFEROUS.
_Mountain limestone_.
_Limestone shale_.

Each of the three principal divisions has its representative in Scotland,
Belgium, and Ireland, but, unfortunately for the last-named country, the
whole of the upper coal-measures are there absent. It is from these
measures that almost all our commercial coals are obtained.

This list of beds might be further curtailed for all practical purposes
of the geologist, and the three great divisions of the system would thus
stand:--

Upper Carboniferous, or Coal-measures proper.

Millstone grit.

Lower Carboniferous, or Mountain limestone.

In short, the formation consists of masses of sandstone, shale, limestone
and coal, these also enclosing clays and ironstones, and, in the