In most localities we do not have to go very far down[14] into the earth to find granite or other so-called igneous rocks, which not only do not contain any traces of fossils, but which we have no proper reason for supposing ever contained any. These Azoic or Archaean rocks constitute practically all the earth's crust, there being only a thin skim of fossiliferous strata on the outside somewhat like the skin on an apple. Now it would be natural enough to suppose that those fossils which occur at the bottom, or next to the Archaean, are the oldest. This is doubtless what the earlier geologists had in mind, or at least ought to have had, for it is not quite certain that they had any clear thoughts on the matter whatever. They did not really begin at the bottom, but half way up, so to speak, at the Mesozoic and Tertiary rocks, and Sedgwick and Murchison, who undertook to find bottom, got too excited over their Cambro-Silurian controversy to attend to such an insignificant detail as the logical proof that any type of fossils was really older than all others. If they had really stopped to consider that some type of fossil might occur next to the Archaean in Wales, and another type occur thus in Scotland, while still another type altogether might be found in this position in some other locality, and so on over the world, leading us to the very natural conclusion that in the olden times as now =there were zoological provinces and districts=, the history of science during the nineteenth century might have been very different, and this chapter might never have been written. But this commonplace of modern geology, that any type of fossil whatever, even the very "youngest," may occur next to the Archaean, was not then considered or understood; and when about 1830 it came to be recognized, other things were allowed to obscure its significance, and the habit of arranging the rocks in chronological order according to their fossils was too firmly established to be disturbed by such an idea. But the Fact Number One, which I have chosen as the subject of this chapter, is the now well established principle that =any kind of fossil whatever, even "young" Tertiary rocks, may rest upon the Archaean or Azoic series, or may themselves be almost wholly metamorphosed or crystalline, thus resembling in position and outward appearance the so-called "oldest" rocks=. The first part of this proposition, about any rocks occurring next to the Archaean, is covered by the following quotation from Dana:[15] "A stratum of one era may rest upon any stratum in the whole of the series below it,--the Coal-measures on either the Archaean, Silurian, or Devonian strata; and the Jurassic, Cretaceous, or Tertiary on any one of the earlier rocks, the intermediate being wanting. The Quaternary in America in some cases rests on Archaean rocks, in others on Silurian or Devonian, in others on Cretaceous or Tertiary."