moth, a gigantic elephant, and the Mastodon, the Zeuglodon, bearing some resemblance to the whale but with great molar-teeth, and the Dinoceras, a huge creature, larger than the rhinoceros, and very similar in habit. our western Prof. Marsh has laid the scientific world under Recent ad- further obligations by additions to this ditions from list taken from the tertiary formations territories. of the "Terres mauvaises" (bad lands) in our western territories. The list includes the Orohippus, Miohippus, and their congeners, in which Prof. Huxley so confidently traces the lineage of the horse. Great plants The plants of the Tertiary, included all the general classes, but the larger proportion of were of the second and third, or the the Tertiary. middle and highest divisions, and approached in form and variety those of the present time. Many of these, also, were of extraordinary size. A fragment of a palm-leaf found in the upper Missouri region, must have measured when complete, twelve feet in length, and there were trees closely related to the giant Sequoias, "big trees," of California. The life of the period was by no means usurped, however, by plants or animals of great size. There are, both in Europe and America, extensive deposits in the rocks of the period, made up almost wholly of siliceous shells, so minute, it is computed by Ehrenberg, that a cubic inch contains more than forty thousand millions. And the nummulitic limestones Infusorial earth. of Southern Europe and Northern Africa, the same of which some of the Egyptian pyramids are built, are made up chiefly of the shells of very minute animals. The forms of life were even more numerous than they had been before, and the most insignificant among them seems to have filled some important place in the economy of the world. And, now, one more upward step in the rock formations and we come to the Age of Quaternary Man). Man, of which there is no need that we Age (Age of speak in much detail. The period is passing now. Intelligence and moral power, other than those concerned in the creation from the first, are become potent factors in the life upon the earth; and all the ambitions and hopes of men find fields of exercise in the tasks it sets before them, and the rewards it holds out to them. [The Quaternary Age will be discussed in Lecture XI.] Our life history of the earth is now complete. found the evidence of plants remaining Review. in the graphite mines, where the plants themselves had disappeared. We found next the simplest class of plants in fossil. Next came a few, sparingly distributed, which rank in the higher class, herbs bearing seed; and lastly, growing side by side with these, the fruit and nut-growing trees. We turned, then, to the animal kingdom. Contemporaneous with these varieties of plants we found the various classes of the animal world. The Protozoan first; a mere "moving thing," almost destitute of organism, but followed in an upward scale by the Radiate (coral), the Mollusk (shell-fish), the Articulate (insect), and the Vertebrate, beginning with the fishes and advancing to the reptile, bird, quadruped, and man. Our task is done. We have read the record in the rocks. Age of the earth. We have made no attempt, it will be observed, to estimate the age of the earth, or to calculate that of any single layer of the rocks. It cannot be done, except approximately, and then with much uncertainty. It is computed it may require a thousand years, under ordinary circumstances, to form a bed of limestone one foot in depth, and possibly five to ten thousand years to form one foot of coal. Lyell estimates the accumulations of the Mississippi delta at about nineteen inches in a century, and that of the Nile mud at less than four inches. Dana computes the most rapid growth of coral reefs at one sixteenth of an inch per annum, and Le Conte estimates it at one to two feet in a century. But all such data are illusive. Two beds of rock forming side by side may differ in their rates of growth, and the same bed may vary from year to year, or century to century. It depends on the material at command, and on the regularity of the currents by which it is deposited. It is comparatively easy to decide which strata are the oldest, by their position or by the fossils they contain. But we know nothing definite of the time required to form them, nor of the time that has elapsed since they were compacted. There are other means of estimating the age of the earth, as a whole, as by its temperature and the erosive action of water, and yet the best authorities differ widely on the subject. A distinguished astronomer estimates the age of the earth since a crust first formed upon it at fifty-seven million years. Sir William Thompson calculates it at one hundred million years. The evolutionists demand more time. They say, whatever may be the necessities of rock formations, that a hundred million years is not sufficient for the Ascidian to develop into a man. We suspect they are correct. But Prof. Proctor would seem to satisfy all reasonable demands in this direction, |