This is distinguished from Mica Slate by the rounded form of the grains of Quartz, and by the Mica lying in separate specks and not in continuous laminae, between the layers or beds of the stone; it is of a more recent formation than the Transition rocks, over which it lies and continues in ninny varieties through the coal formation; several form a sort of slate and serve for roofing houses, &c. others are stratified in a trough way, much resembling Gneiss, and in many instances they contain fragments of Feldspar in a more or less decomposed state; it varies in colour, being of a red brown, sometimes lighter or yellower, and where it appears to be near the coal formation, charcoal is very distinct in it. In some places, as at Dundee, in Scotland, there is a brown micaceous sandstone that is brought occasionally to London in immense blocks for some of the bridge and canal works, &c. where also, some of the Yorkshire strata are used; the former contains a clayey shale in larger or smaller masses, almost free from Mica.
The micaceous sandstones seem, according to Geologists, in a great measure to designate formations; thus the coarse ones and those without petrifactions are generally the oldest; those of a finer grain with vegetable remains and Clay or Shale, belong to the coal formation; the latest, is, perhaps, that which contains siliceous casts of shells, as that of Devonshire.
The principal figure in the plate is a fragment of Yorkshire Flag-stone, such as is used for paving in London; the best kind contains much less Mica and is a very durable stone. The right hand figure is from a specimen containing decomposed Feldspar. The left hand figure, a specimen from the neighbourhood of Coal; it contains the Charcoaly remains of some plant, the bituminous parts of which have probably entered into the composition of the coal. The lower figure is from a piece of the kind brought from Dundee, with Slate Clay, or Shale attached to it.