mass of limestone and dolomite, the Durness limestone (1500 ft.). In
the lower series are, in descending order, the "Serpulite grits" or
"Salterella beds," the "Fucoid beds" and the "Eriboll quartzite,"
which is divided into an upper "Pipe rock" and lower "Basal
quartzite."

The Cambrian rocks of _Ireland_, a great series of purple and green
shales, slates and grits with beds of quartzite, have not yet yielded
sufficient fossil evidence to permit of a correlation with the Welsh
rocks, and possibly some parts of the series may be transferred in the
future to the overlying Ordovician.

_North America._--On the North American continent, as in Europe, the
Cambrian system is divisible into three series: (1) the lower or
"Georgian," with _Olenellus_ fauna; (2) the middle or "Acadian," with
_Paradoxides or Dikelocephalus_ fauna; (3) the upper or "Potsdam,"
with _Olenus_ fauna (with Saratogan or St Croix as synonyms for
Potsdam). The lower division appears on the Newfoundland and Labrador
coasts, and is traceable thence, in a great belt south-west of those
points, through Maine and the Hudson-Champlain valley into Alabama, a
distance of some 2000 m.; and the rocks are brought up again on the
western uplift, in Nevada, Idaho, Utah, western Montana and British
Columbia. The middle division covers approximately the same region as
the lower one, and in addition it is found in the states of Texas,
Oklahoma, and Arizona, in western Montana, and possibly in western
Wisconsin. The lower division, in addition to covering the areas
already indicated, spreads over the interior of the United States.

_Bohemia_.--The Cambrian rocks of this country are now recognized by
J.F. Pompesk; to comprise the Paradoxidian and Olenelledian groups.
They were made famous through the researches of Barrande. The Cambrian
system is covered by his stages "B" and "C"; the former a barren
series of conglomerates and quartzites, the latter a series of grey
and green fissile shales 1200 ft. thick with sandstones, greywackes
and conglomerates.

+----------------+--------------------+---------------+----------------------------------------------------------------+
| | | | Midland and West of England. |
| | North Wales. | South Wales. +--------------------+---------------------+----------