39 



which divides North America into natural provinces, in each of which the 

 conditions of environment are hroadly uniform. What these conditions 

 are. may he seen by a comparison of No. 4 with Nos. 1, 2 and 3. 



North America In its world relations stands among the continents 

 third In area and fourth in population. It. is built on the triangular plan, 

 presenting to the Pacific a high and forbidding back, but facing the At- 

 lantic with a low and inviting coast. The body of it is made up of the 

 largest continuous plain in the world, one-third of the continent being 

 less than OOO feet above the sea. Its shores are washed by all the oceans 

 of the northern hemisphere, and it is crossed by all belts of climate (Fig. 

 2). It contains an assemblage of land forms which include all varieties 

 of structure, relief and mineral i>roducts. It would be difficult to name a 

 plant or animal which could not find a congenial home in some part of it. 

 More than half of it lies in those middle latitudes which are most favorable 

 for a high degree of civilization. Its position, extent, character and com 

 plexity render it one of the most valuable assets of the human race on this 

 planet. It constitutes by itself a world in which nothing essential for 

 human welfare is lacking. 



In the scientific study of enviroHinents extremes are the simplest. 

 In provinces controlled by one dominant factor, such as the ocean, heat, 

 cold, aridity or vertical elevation, the outlines of the pictures are clear 

 and bold. Environmental influence and organic reaction, "Ihe reciprocal re- 

 lations of organisms and the external world," are apparent at a glance 

 and leave little that is elusive or con.iectural. 



Greenland, the largest of islaiids, a broken block plateau capped witii 

 ice, is an absolute desert except ai'ound the margins, where a fringe of 

 barren rock affords a perching ])lace foi- sea fowls and Eskimos. Around 

 its shores the lithosphere c(wers the hydrosphere in the fiu'ni of a shifting 

 crust of pack ice, where the seal, walrus, polar bear, and man live as 

 ice-riding animals. The basis of subsistence is found in the water, which 

 teems with life from microscopic infusoria to whales. Upon these birds and 

 beast subsist, and man upon all of them. ^Metals are absent and vegetable 

 material is negligible. The kayak, the harpoon pointed with a walrus 

 tusk and tied with a rawhide-line to a bladder float, sealskin clothing, 

 tents and boats, bone sledges, the snow igloo built in an hour and frost 

 and bear proof, the artic dog sleeping in all wt^athers with only his tail 

 for a cover, blubber food and fuel, and the skill which men have acquired 



