the southern portion of Florida and its keys. Since then the latter have grown and are still growing. [Illustration: FIG. 13.—Early Tertiary North America. From Shaler’s First Book in Geology. By courtesy of the publishers, D. C. Heath & Co.] A later epoch still in the history of the globe is known as the =Quaternary= period, the period that immediately preceded our present epoch. The great features of this period, which is divided into =Glacial=, =Champlain= and =Terrace= epochs, are the wide-spread oscillations of the earth’s crust in high latitudes towards the north and south poles, attended with great changes of climate from temperateness to extreme cold. The Glacial epoch was characterized by upward crust movements, the land becoming over one thousand feet higher than at present. The land was covered with ice, and an arctic severity of climate extended almost to the Gulf of Mexico. The Champlain epoch was characterized by a downward movement of the coast until it became five hundred feet or more below the present level, so that many lower portions of the continent became covered with sea. At this time there was a moderation of the temperature, a melting of the vast sheets of ice, and consequently a flooding of rivers and lakes, with many icebergs floating in them. The last or Terrace epoch of the Quaternary period was characterized by a crust movement up to the present condition of things. What is true of the instability of the North American Continent is true of _all_ the continents of the globe. They have all grown from small beginnings to their present huge proportions, and are _now_ undergoing slow but irresistible changes. When these facts are held in mind, one may form a faint conception of the colossal changes that have taken place throughout the sweep of bygone ages. _Environment means a complexity of conditions almost infinite in their number and character, and almost infinite in their variations._ SECTION IV. TRANSMUTATION OF LIVING FORMS. TRANSMUTATION OF LIVING FORMS.