|(continental |
| | (marine littoral) | type) | type) |
+-------------+------------------------+---------------+-------------+
| America. | Missippian | Pennsylvanian |
+-------------+------------------------+---------------+-------------+
| Predominant | Lycopods. | Sigillarias | Ferns and |
| Plant Types.| | and Calamites | Annularias |
+-------------+------------------------+---------------+-------------+

In the eastern border of the Rhenish Schiefergebirge the Permian rests
unconformably upon Lower Carboniferous rocks. In the United States, in
Missouri, Pennsylvania, West Virginia, Kentucky, Ohio and elsewhere,
there is an unconformable junction between the Lower and Upper
Carboniferous, representing an interval of time during which the lower
member was strongly eroded; it has even been proposed to regard the
Mississippian (Lower Carboniferous) as a distinct geological period,
mainly on account of this break in the succession.

_Thickness of Carboniferous Rocks._--The great variety of conditions
under which the sediments and limestones were formed naturally
produced corresponding inequalities in the thickness. In the Eurasian
land area the greatest thickness of Carboniferous rocks is in the
west; in North America it is in the east. In Britain the Carboniferous
limestone series is 2000-3500 ft. thick; in the Ural mountains it is
over 4500 ft.; the Culm in Moravia is credited with the enormous
thickness of over 42,000 ft. The Upper Carboniferous in Lancashire is
from 12,000 to 13,000 ft.; elsewhere in Britain it is thinner. In
western Germany this portion attains a thickness of 10,000 ft. In
Pennsylvania the sandstone and shale, at its maximum, reaches 4400
ft., but even within the limits of the state this formation has
thinned out to no more than 300 ft. in places. In Colorado the Lower
Carboniferous is only 400-500 ft. thick; while the limestones of the
Mississippi basin amount to 1500 ft. and in Virginia are 2000 ft.
thick.

_Life of the Carboniferous Period._--We have seen that in the
Carboniferous rocks there are two phases of sedimentation, the one
marine, the other continental; corresponding with these there are two
distinct faunal facies.

(1) _Fauna of the Marine Strata._--Numerically, the most important
inhabitants o