Audio File   THE LAST GREAT MAMMALIAN MIGRATION This is the period of preglacial land elevation in North America, Europe, and Asia. The land was greatly altered in topography. Mountain ranges were born, streams changed [More]
Audio File THE AGE OF EARLY MAMMALS   50,000,000 years ago, the land areas of the world were very generally above water or only slightly submerged. The formations and deposits of this period are both land [More]
Audio File   The continental land drift continued. The earth’s core had become as dense and rigid as steel, being subjected to a pressure of almost 25,000 tons to the square inch, and owing to [More]
Audio File   Accompanied by little or no volcanic action, the periodic phenomena of land elevation and land sinking characteristic of these times were all gradual and nonspectacular. Throughout all of these successive land elevations [More]