shining black, or entirely lost. In the last mentioned case, only the impression remained, but the carbonaceous matter had gone to stain the surrounding clay black, thus indicating that the dark colour of the coal-shales is due to the carbon derived from the plants which they included.
Another very prominent member of the vegetation of the coal period, was that order of plants known as the Calamites. The generic distinctions between fossil and living ferns were so slight in many cases as to be almost indistinguishable. This resemblance between the ancient and the modern is not found so apparent in other plants. The Calamites of the coal-measures bore indeed a very striking resemblance, and were closely related, to our modern horse-tails, as the equiseta are popularly called; but in some respects they differed considerably.
Most people are acquainted with the horse-tail (_equisetum fluviatile)_ of our marshes and ditches. It is a somewhat graceful plant, and stands erect with a jointed