scattered about like those of early Scottish history, all hope of ever attaining to anything like a correct chronology and arrangement would have to be abandoned in despair. In truth, it would then be impossible to conjecture whether any succession of ages preceded man, during which other tribes of plants and animals lived and died, or whether the whole mass of fossiliferous rocks had been accumulated since the human era, or perhaps created just as we find them. But all this uncertainty and confusion has been obviated simply by the fossils being ranged in beds vertically above each other, the oldest at the bottom and the latest at the top. So that if we find in a low cliff along the shore blown sand and broken whelks immediately beneath the vegetable mould, and oyster-valves in a clayey bed three feet below, we pronounce the oysters to have lived before the whelks, and that between their respective lifetimes a sufficient interval must have elapsed to allow three feet of sand, clay, and gravel, to accumulate. What is thus true on the small scale holds equally so on the large. The stratified formations in which organic remains occur are found to be grouped regularly over each other in a settled invariable order. If A be below B in England it will be below B all over the world, and if C be above D at the North Pole it will be so at the South Pole too, and at every locality where the two rocks lie together. This order of superposition forms one of the grand tests for the age of different rock masses. By means of this simple rule the geologist has been enabled to arrange the different stratified formations, supplying the missing portions of one locality from the more complete series of another, so as to form a chronological table of no small part of our planet's primeval history. [Footnote 57: See Dr. Daniel Wilson's deeply interesting work _The Pre-historic Annals of Scotland_.]