How long was this first or Eozoic period? That, no one can tell. If we should try to tell, we should merely use numbers so great that, as applied to years, we cannot imagine them. The Dawn age seems a very good name for it, as it was the age of the earliest continents, and of the first animal and vegetable life. As the study of the earth goes on, and other and deeper-lying rocks are examined, we may learn much more about this first world-building period. Now, as we look far, far back to it, it strikes us, I think, chiefly as distant, barren, silent. If we had been Afrites, and hovering over that early continent, I think we should not have heard a sound, except the lap of the warm waves on the rocks; we should not have seen a living thing. But if instead of Afrites we had been Pixies, or water-sprites, we should have gone down into the waters of that wide, warm sea, and what should we have found? We can as well fancy ourselves Pixies as Afrites. Let us fancy ourselves in those seas. I think we should have seen sea-weeds, fine and small, but of many curious shapes, and millions of creatures with and without shells, some large, some small, tinted like rainbows, and lively and happy in their water-world. FOOTNOTES: [3] Primary, Secondary, Tertiary, Quaternary. [4] Eozoic, Paleozoic, Mesozoic, Cenozoic. [5] Nature Reader, No. 2, Lessons 36 and 37. [6] Nature Reader, No. 1, Lesson 37. [7] Nature Reader, No. 3, Lesson 1. [8] And after all so few and indefinite are the traces, that Eozoön may not have been an animal form at all, but a merely mineral structure. LESSON III. THE AGE OF CRABS AND CORALS. “And delving in the outworks of this world And little crevices that they could reach, Discovered certain bones laid up and furled Under an ancient beach.” --INGELOW. The earth-building period which followed the dawn of life is called the “time of ancient life.” Our lesson about this period will be like unlocking the gate to some beautiful domain, giving a glance at its delights, but leaving the wayfarer whom we have brought thus far on his journey, still standing without, yet now, no doubt, with ability and desire to enter. This ancient-life time is, so far as we know, the longest of all the earth-building periods. It has the thickest deposits of rock, and includes the most numerous ages, or great successive changes. It also retains in its rocks numerous fossils, or casts of formerly living things, both animal and vegetable. In coming lessons we shall discuss what fossils are, and describe some of these ancient plants and animals. [Illustration: THE WATER-SPRITES.]