While Murchison and Sedgwick were prosecuting their inquiries into the Silurian rocks, Hugh Miller and many others had their attention occupied with the Old Red Sandstone--the Devonian of Sedgwick and Murchison--which immediately overlies them. After a youth passed in wandering among the woods and rocks of his native Cromarty, the day came when Miller found himself twenty years of age, and, for the time, a workman in a quarry. A hard fate he thought it at the time, but to him it was the road to fame and success in life. The quarry in which he laboured was at the bottom of a bay formed by the mouth of a river opening to the south, a clear current of water on one side, as he vividly described it, and a thick wood on the other. In this silent spot, in the remote Highlands, a curious fossil fish of the Old Red Sandstone was revealed to him; its appearance struck him with astonishment; a fellow-workman named a spot where many such monuments of a former world were scattered about; he visited the place, and became a geologist and the historian of the “Old Red.” And what strange fantastic forms did it afterwards fall to his lot to describe! “The figures on a China vase or Egyptian obelisk,” he says, “differ less from the real representation of the objects than the fossil fishes of the ‘Old Red’ differ from the living forms which now swim in our seas.” The _Carboniferous Limestone_, which underlies the coal, the _Coal-measures_ themselves, the _New Red Sandstone_, the _Lias_, and the _Chalk_, have in their turn found their historians; but it would be foreign to our object to dwell further here on these particular branches of the subject. Some few of the fossilised beings referred to resemble species still found living, but the greater part belong to species which have become altogether extinct. These fossil remains may constitute natural families, none of the genera of which have survived. Such is the _Pterodactyle_ among Pterosaurian reptiles; the _Ammonite_ among Mollusca; the _Ichthyosaurus_ and the _Plesiosaurus_ among the Enaliosaurian reptiles. At other times there are only extinct genera, belonging to families of which there are still some genera now living, as the genus _Palæoniscus_ among fishes. Finally, in Tertiary deposits, we meet with some extinct species belonging to genera of our existing fauna: the _Mammoth_, for example, of the youngest Tertiary deposits, is an extinct species of the genus elephant. Some fossils are terrestrial, like the gigantic Irish stag, _Cervus Megaceros_, the snail or _Helix_; fluviatile or lacustrine, like the _Planorbis_, the _Lymnæa_, the _Physa_, and the _Unio_; marine, or inhabiting the sea exclusively, as the Cowry (_Cypræa_), and the Oyster, (_Ostrea_).