When we were speaking of the coal-mines I told you something about the remains of giant ferns, sedges, reeds, and mare's-tails of far larger growth than any now known, which have been found there. You are familiar with fossil-plants, but I do not think we have spoken much of fossil-animals, which are found in all except the oldest layers of rock--the first pages of the "Stone Book." The children had been with me to the Museum in the town in which we lived, and had looked with wonder at the huge creatures whose skeletons have been built up bone by bone, after being taken from their rocky tomb--for this earth of ours which has seen so many changes has been rifled of her treasures; not the gold and silver, coal and iron with which she is so richly stored, but the wonderful specimens of God's work in bygone ages which He has allowed us to see; so that we cannot doubt that such creatures once existed, though we may know nothing with certainty as to the time of their first appearance in the sea and on the dry land, and can only guess at the kind of life they lived. You remember that we spoke, in the chapter about the earth's crust, of the "fire-made rocks," which were once in a liquid state from intense heat (we could not expect to find any remains of plants or animals there, and none _have_ been found), and of the "water-made rocks," which have been gradually accumulated by the action of water in wearing down the land. These rocks lie in layers, and fossil shells, plants, and bones of animals have been found in them, as we have already seen. But how did these fossils get into the rocks? And how is it that they have been found in all countries and at all heights above the sea? Before I try to answer these questions, I must tell you that when geologists speak of "rock" they mean everything which has gone to form the crust of the earth, whether clay, or loose sand and gravel, or the hard heavy granite which some of us had seen crowning the Dartmoor tors.