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Blith's book is the first systematic work in which there are some traces of alternate husbandry or the practice of interposing clover and turnip between culmiferous crops.

It was not until the year 1836 that Sir R. Murchison and Professor Sedgwick discovered that the culmiferous or anthracitic shales and sandstones of North Devon, several thousand feet thick, belonged to the coal, and that the beds below them, which are of still greater thickness, and which, like the carboniferous strata, had been confounded under the general name "graywacke," occupied a geological position corresponding to that of the Old Red Sandstone already described.