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 162 Conchology). In 1830, when composing the article Geology for the Encyclopædia Metropolitana, (published 1833,) my attention was caught by the singular fact of the classification of these Devonian rocks among the transition (Silurian) strata, while the fossils then known bore a great analogy to those of the mountain limestone; and I could not avoid expressing a strong doubt that these strata were really of so high antiquity. The doubt was more than confirmed (in 1837-40) by the united labours of Murchison, Sedgwick, and Lonsdale, the result being the establishment., by Mr. Lonsdale, of an intermediate group of fossils in an intermediate group of strata,—the now well-known 'Devonian system' (''Geol. Trans.'', 1837 to 1840).

In 1837, Murchison, in his 'Silurian System,' raised, for the first time, the old red to the rank of a system, and in 1842 completed the evidence on this subject by an examination of Russia. Since that time the Devonian system has been generally adopted.

Yet still we must not forget that a strong physical relationship binds together the peroxidated old red to the protoxidated blue shales of the mountain limestone; that in all the districts of Britain they are in parallel deposits; and that beds of red sandstone enter into the composition of the lower limestone series in the north of England.

Composition.—Six substances are interstratified in this system: arenaceous, argillaceous, and calcareous rocks form the principal masses, and are associated with beds of chert, ironstone, and coal. Some of the arenaceous rocks are conglomerates, as millstone grit, which is partially filled with quartz, felspar, and fragments of shale, the mingled spoils of granitic rocks, quartz veins, and schists; others are freestones of an open grain and equal texture, breaking equally in all directions; others are compact close grits, called hazle; or still finer grained, called calliard; or laminated with mica, or carbonaceous matter,