The Paleozoic strata (not including igneous bed), 57,154 feet. Secondary, 13,190 ,, Tertiary, 2,240 ,, making altogether 72,584 feet; that is, very nearly thirteen and three-quarters British miles. Büchner in his work on "Force and Matter" states: "The so-called coal formation alone required, according to Bischoff, 1,000,177 years; according to Chevandier's calculation, 672,788 years. The Tertiary strata required for their development about 350,000 years; and before the originally incandescent earth could cool down from a temperature of 2,000 degrees to 200, there must, according to Bischoff's calculation, have elapsed a period of 350,000,000 years. Valger calculates that the time required for the deposit of the strata known to us must at least have amounted to 648,000,000 years. I quote these figures simply to show how difficult it is, and the labor required, to form even a proximate idea as to the period of time that must have elapsed for the formation of the various strata known. That all animals were not created at once is certain beyond all cavil and dispute. The development of the various forms of life was an exceeding slow process, and lasted very many thousand centuries. That the earth's crust was not at certain stages of formation in a fit condition either to receive or to maintain the higher types of animal life, is well known. And we know that man's remains are found only in the uppermost surface of the earth's crust. Max Müller says in his "Testimony of the Rocks": "It was not until the earlier ages of the Oölite system had passed away, that the class of Reptiles received its fullest development. And certainly very wonderful was the development which it did then receive. Reptiles became everywhere the lords and masters of the lower world. When any class of air-breathing vertebrates is very largely developed, we find it taking possession of all three terrestrial elements--earth, air, and water. Last of all, the true placental mammals appear, and thus, tried by the test of perfect reproduction, the great vertebral division receives its full development." Agassiz's "Principles of Zoology" says: "We distinguish four ages of nature, comprehending the great geological divisions, namely: "1. The Primary, or Paleozoic age, comprising the lower Silurian, the upper Silurian, and the Devonian. During this age there were no air-breathing animals. The fishes were masters of creation. We may therefore call it the Reign of Fishes. "2. The Secondary age, comprising the Carboniferous, the Trias, the Oölite, and the Cretaceous formations. This is the epoch in which air-breathing animals first appear. The Reptiles predominated over the other classes, and we may therefore call it the 'Reign of Reptiles.' "3. The Tertiary age, comprising the Tertiary formation. During this age terrestrial mammals of great size abound. This is the Reign of Mammals.