l and Keyserling, rocks intermediate between the Upper
Silurian and Carboniferous Limestone formations cover an extent of
surface larger than the British Islands. This wide development arises
not from the thickness but from the undisturbed horizontal character
of the strata. Like the Silurian formations described elsewhere, they
remain to this day nearly as flat and unaltered as they were
originally laid down. Judged by mere vertical depth, they present but
a meagre representative of the massive Devonian greywacke and
limestone of Germany, or of the Old Red Sandstone of Britain. Yet vast
though the area is over which they form the surface rock, it is
probably only a small portion of their total extent; for they are
found turned up from under the newer formations along the flank of the
Ural chain. It would thus seem that they spread continuously across
the whole breadth of Russia in Europe. Though almost everywhere
undisturbed, they afford evidence of some terrestrial oscillation
between the time of their formation and that of the Silurian rocks on
which they rest, for they are found gradually to overlap Upper and
Lower Silurian formations.

TABLE I.

+-------------+-------------------+------------------------------+--------------+-----------------+-----------------+
| | | | Brittany and | | |
| Stages. | Ardennes. | Rhineland. | Normandy. | Bohemia. | Harz. |
/ +-------------+-------------------+------------------------------+--------------+-----------------+-----------------+
| | | Limestone of | Cypridina slates. | Slates of | | Cypridina |
U | | | Etroeungt. | Poen sandstone (Sauerland). | Rostellec. | | slates. |
P | | Famennien | Psammites of | Crumbly limestone (Kramen- | | | Clymenia |
P | | (Clymenia | Condroz (sandy | zelkalk) with Clymenia. | | | limestone and |
E | | beds). | series). | Neheim slates in Sauerland, | | | limestone of |
R | | | Slates of Famenne | and diabases, tuffs, &c., | | |