356 POPULAR SCIENCE MONTHLY. 



flowed outward on all sides from this great plateau. Bowlders 

 from its rock formations were then borne by the slow glacial cur- 

 rents eastward to the head waters of the Volga, southward to the 

 Dnieper and the Rhine, and south westward to the northeastern 

 shore of England, where the confluent current of the ice flowing 

 away from the Scottish Highlands warded off the Scandinavian 

 ice after its passage over the bed of the shallow North Sea. The 

 European ice sheet extended south only to the latitude of 50, 

 while that of our continent reached to 38 in southern Illinois ; 

 but the difference was similar to the present contrast of the mean 

 annual temperature and isothermal lines of the two continents. 



To-day the Greenland ice sheet, the Malaspina ice sheet be- 

 tween Mount St. Elias and the ocean, many glaciers southward 

 along the Cordilleran mountain belt, and the ice fields and glaciers 

 of Norway and the Alps, may be regarded as lingering repre- 

 sentatives of the conditions of the Glacial period, which not long 

 ago, geologically speaking, spread a white pall of snow and unin- 

 habitable desolation over large parts of the earth that are now 

 temperate, fruitful, and populous. The returning mild and habit- 

 able conditions, with luxuriant plant and animal life, are like the 

 average of long geologic eras which preceded the Ice age, and 

 were of far greater and indeed almost inconceivable duration. 

 The severely cold and snowy Glacial climate of extensive land 

 areas was wholly unlike their mild or even hot climates during 

 the very long Tertiary and Mesozoic eras, of which we find testi- 

 mony in their fossil floras and faunas. Palms allied to those of 

 the tropics, and sequoias closely related to the big redwood trees 

 of California, grew during Tertiary times in Greenland, Spitz - 

 bergen, and the New Siberia Islands. Baron Nordenskjold, after 

 examining thousands of miles of arctic shore lines, with frequent 

 clearly exposed geologic sections belonging to the periods extend- 

 ing back from the Ice age through the Tertiary or Cenozoic, the 

 Mesozoic, and the Palaeozoic eras, affirmed that he nowhere dis- 

 covered any evidence of glaciation previous to the Pleistocene 

 period, which followed the Tertiary and introduced the Quater- 

 nary era. 



Latest in the great series of periods made known by the geo- 

 logic record, the Pleistocene or Glacial period stands alone and 

 unique, unless we must also recognize a general prevalence of gla- 

 cial conditions at or near the end of the Palaeozoic era. Bowlder- 

 bearing deposits which can be explained only as glacial drift, and 

 striation of the underlying rock which testifies unmistakably of 

 the action of great glaciers or sheets of land ice, are found in the 

 Carboniferous or the Permian series, closing the Palaeozoic sys- 

 tem, in Britain, France, and Germany, Natal, India, and south- 

 eastern Australia. In Natal the striated glacier floor is in latitude 



