The commonly-received theory that most coal-seams represent vegetable matter that has grown and has been entombed on the spot has never been received by all geologists with quite that measure of satisfaction that has been accorded to other theories of the same general nature. It has been felt again and again that the explanation referred to might be true enough for certain cases; but that in others it failed to account satisfactorily for all the phenomena. It involved too many complications—too nice an adjustment of the rate of growth of the vegetation to the rate of subsidence and of sedimentation—too much straining of the theory in question generally—to be accepted unhesitatingly by those accustomed to judge of such facts for themselves. That certain beds of coal have been formed by the growth of vegetation on the spot no reasonable person can doubt: the only question is whether that is true of every coal-seam.