een found at Dover.

From England, Carboniferous rocks can be followed across northern and
central France, into Germany, Bohemia, the Alps, Italy and Spain. In
Russia this system occupies some 30,000 sq. m., and it extends
northward at least as far as Spitsbergen. Carboniferous rocks are
present in North and South Africa, and in India and Australasia; in
China they cover thousands of square miles, and in the United States
and British North America they occupy no less than 200,000 sq. m.;
they are known also in South America.

The subjoined table expresses the typical subdivisions which can be
recognized, with modifications, in the United Kingdom.

/ Upper: Red and grey sandstones, marls and clays with
| occasional breccias, thin coals and limestones with
| _Spirorbis_, workable coals in the South Wales,
| Bristol, Somerset and Forest of Dean coalfields.
Coal |
Measures. < Middle: Sandstones, marls, shales and the most
| important of the British coals.
|
| Lower: Flaggy hard sandstones (ganister), shales and
\ thin coal seams.

/ Grits (coarse and fine), shales, thin coal seams and
Millstone < occasional thin limestones. The fossil plants connect
Grit. | this group with the coal-measures; the marine fossils
\ have, to some extent, a Carboniferous limestone aspect.

/_Upper black shales_ with thin limestones (Pendleside
| group) connecting this series with the Millstone grit
| above.
|
| _The thick, main or scaur limestone_ (mountain
| limestone) of the centre and south of England, Wales
| and Ireland, which splits up in the Yorkshire dales
Carboniferous | (Yoredale group) into a succession of stout limestone
Limestone < beds between beds of sandstone and shale, and becomes
Series. | increasingly detrital in character as it is traced
| northwards.
|
| _Lower limestone shales_ of the south and centre of
| England with marine fossils, and the Calciferous
| Sandstone group of Scotland with marine, estuarine and
\terrestrial fossils.

(See BERNICIAN, TUEDIAN and AVONIAN.)

At an early period, owing to the immen