doubt the importance and
reality of the Devonian series as an independent system of rocks
to be intercalated in point of time between the Silurian and
the Carboniferous. The want of agreement, both lithologically
and palaeontologically, between the Devonian and the Old Red,
can be explained by supposing that these two formations, though
wholly or in great part _contemporaneous_, and therefore strict
equivalents, represent deposits in two different geographical
areas, laid down under different conditions. On this view, the
typical Devonian rocks of Europe, Britain, and North America are
the deep-sea deposits of the Devonian period, or, at any rate, are
genuine marine sediments formed far from land. On the other hand,
the "Old Red Sandstone" of Britain and the corresponding "Gaspe
Group" of Eastern Canada represent the shallow-water shore-deposits
of the same period. In fact, the former of these last-mentioned
deposits contains no fossils which can be asserted positively
to be _marine_ (unless the Eurypterids be considered so); and
it is even conceivable that it represents the sediments of an
inland sea. Accepting this explanation in the meanwhile, we may
very briefly consider the general succession of the deposits of
this period in Scotland, in Devonshire, and in North America.

In Scotland the "Old Red" forms a great series of arenaceous and
conglomeratic strata, attaining a thickness of many thousands of
feet, and divisible into three groups. Of these, the _Lower Old
Red Sandstone_ reposes with perfect conformity upon the highest
beds of the Upper Silurian, the two formations being almost
inseparably united by an intermediate series of "passage-beds."
In mineral nature this group consists principally of massive
conglomerates, sandstones, shales, and concretionary limestones;
and its fossils consist chiefly of large crustaceans belonging to
the family of the _Eurypterids_, fishes, and plants. The _Middle
Old Red Sandstone_ consists of flagstones, bituminous shales,
and conglomerates, sometimes with irregular calcareous bands;
and its fossils are principally fishes and plants. It may be
wholly wanting, when the _Upper Old Red_ seems to repose
unconformably upon the lower division of the series. The _Upper
Old Red Sandstone_ consists of conglomerates and grits, along
with a great series of red and yellow sandstones--the fossils,
as before, being fishes and remains of plants. The Upper Old
Red graduates upwards conform