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 conformably into the Carboniferous series.
The Devonian rocks of Devonshire are likewise divisible into a
lower, middle, and upper division. The _Lower Devonian_ or _Lynton
Group_ consists of red and purple sandstones, with marine fossils,
corresponding to the "Spirifer Sandstein" of Germany, and to the
arenaceous deposits (Schoharie and Cauda-Galli Grits) at the base
of the American Devonian.
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