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 196 system, that in the upper strata a general analogy to the oolitic æra can be recognised by the trigoniæ, plagiostomata, ostreæ, &c.; and by their productæ and spiriferæ the lower strata as distinctly claim affinity with the carboniferous limestone. While composing my work on the Palæozoic Fossils of Devon and Cornwall (published 1841) the lower group came necessarily under review, and I concluded that in respect of organic life its affinity was really with the carboniferous limestone, though its mineral association was with the new red. This view is now generally adopted ; and Murchison, De Verneuil and Keyserling, by a large examination in Russia of strata which are the equivalents there of the magnesian limestone of England and Germany, have founded on these strata the Permian system.

Composition.—After examining the carboniferous rocks, the red sandstones and the associated strata present themselves with an air of novelty and freshness, not less striking to the geologist than a new country to the traveller. Instead of the black, blue, or grey limestone, full of crinoidal columns, products, &c., we have now yellow, sandy, or granular rocks, with few organic remains: the dark shales of the coal series are exchanged for red, green, and blue marls, and the micaceous yellow, ochraceous or brown grits, for red or white sandstones. On a general view the contrast is sharp and defined, even where the strata of the two groups are parallel, but close examination points out several instances (Manchester and Salop) of transition coal deposits, in which red grits and clays inclose coal, with shales and limestones of a peculiar aspect.

The limestones of this system vary much. They are often loaded with magnesia, and in general called "magnesian limestone;" but there are many beds in which little or no foreign admixture deteriorates the carbonate of lime. The colours are white, grey, smoky, but more frequently yellow; and in some districts reddened, or