tion
by different workers include brachiopods, pelecypods, cephalopods,
corals, fishes and plants; and the results of the comparison of the
faunas and floras of different areas where Carboniferous rocks occur
are generalized in the table below.

The relative value of any group of animals or plants for the
correlation of distant areas must vary greatly with the varying
conditions of sedimentation and with the precise definition of the
zonal species and with many other factors. It is found that the
subdivisions in this system demanded by palaeobotanists do not always
coincide with those acknowledged by palaeozoologists; nevertheless
there is general agreement as to the main divisional lines.

_Breaks in the Stratigraphic Sequence._--The sequence of Carboniferous
strata is not everywhere one of unbroken continuity. From central
France eastward towards the Carpathians only later portions of the
system are found. These generally rest upon crystalline rocks, but in
places they contain evidence of the denuded surfaces of Lower
Carboniferous, as in the basin of Charleroi, where the equivalent of
the Millstone Grit contains fragments of chert which can only have
come from the waste of the earlier limestones. This unconformity is
generally found about the same horizon in the continental Culm areas,
and it occurs again in the western part of the English Culm.

_Tabular Statement of the Principal Subdivisions of the Carboniferous
System._

+-------------+------------------------+---------------+-------------+
| | Lower Carboniferous | Upper Carboniferous |
+-------------+------------------------+---------------+-------------+
| | Carboniferous | Coal Measures = |
| | Limestone Series. | Terrain Houiller. |
+-------------+------------------------+---------------+-------------+
| | Dinantien = | Moscovien = | Ouralien = |
| | (marine pelagic, | (marine type) |(marine type)|
| | including continental | | |
| European | deposits in some areas)| and | and |
| Development.| and | | |
| | | Westphalien = | Stephanien =|
| | Culm = |(continental