xii EXPLANATION OF THE FRONTISPIECE. In Fifeshire, one of the middle counties of Scotland, the Carboniferous system lies on the Devonian. In Durham the Oolitic lies on the New Red Sandstone, and the Cretaceous lies on the Oolitic; while in the county of Kent the Tertiary rocks overlie the Cretaceous. Hence, though we do not find all the series occurring at any one place, the sections that do occur are always like the plan given. Hence this order of rocks has been termed the key to solve all the problems in geological science. Let the reader find one of the rocks as given in the frontispiece, in any country whatever, and he will at once know the position of that rock in the earth's crust, no matter where found. But in some cases mineral character will fail him; a sandstone from the Oolitic series may not be distinguishable from the millstone grit of the coal measure. He must then have recourse to the fossils; and finding these, he will soon be enabled to say whether he is in an Oolitic or a Carboniferous country. The fact that certain fossils are always found in certain rocks, has suggested the idea of dividing the sedimentary rocks into great divisions according to the fossils which are found within them. Hence a certain class of fossils are found to be recent, occurring in the Tertiary rocks, so they are called Cainozoic, or recent life. A different class of fossils are found in the secondary rocks; they are called Mesozoic, middle life. These are reptiles, commonly called Saurian Reptiles. In Scripture they are the great whales and living creatures that hath life." Earlier fossils are called Paleozoic, that is ancient life, so called because it is much longer since they were extinct. The latest class of these are called Amphibians, because EXPLANATION OF THE FRONTISPIECE. xiii they could live on land or in water. Before these, were fishes, the Placoids and Ganoids of Devonian waters. The Brachiopoda were the molluscs, or shell-fishes of the Silurian period. The Hydrozoa, so called because they are allied to the Hydra, and include the zoophytes, &c., of Cambrian seas. The Protozoa, being the lowest division of the animal kingdom. Here the order refers specially to the Eozoon of the Laurentian rocks in Canada. Let the reader carefully consider this scale of rocks as given in the frontispiece, and that will help him in his study of Geology. |