HARVESTING THE FOREST CROP 119 



Owing to the fact that the mountain chains in North 

 America run north and south, many tree species escaped 

 extinction during the glacial period when the northern 

 portion of the United States was covered with a sheet 

 of ice. 



In Europe, where there are but one hundred tree 

 species against the five hundred upon this continent, the 

 mountain barriers run east and west, and so when the 

 tree communities were blotted out by the enormous ice 

 sheets, certain species were not able to surmount the 

 mountain ranges and thus regain the ground they for- 

 merly occupied. 



Forest Regions. The study of the original forests of 

 this continent is most interesting, and from forest re- 

 mains found in rocks far beneath the surface, it is 

 known that certain species now quite limited in their 

 range once were distributed over a wide stretch of 

 country. The redwood now occupying a thin belt along 

 the coast range of California was once found far in 

 toward the Rocky Mountains and also flourished in 

 Europe and Western Asia. 



The Pacific Northwest then, as now, was covered with 

 dense forests in which hemlock, cedar, and the firs 

 predominated, massive timber above and dense under- 

 growth, holding the world's record for uniform den- 

 sity. Passing to the east, the Rocky Mountain forest, 

 containing lodgepole and yellow pine, or Douglas and 

 white fir, or Englemann spruce, depending upon lati- 

 tude or elevation, soon gives way to the treeless plains. 

 Here mile after mile of open grassy plains are found 

 and the early emigrant bound for California stopped 

 his prairie schooner and made camp along the water 

 courses, since there only could firewood be secured from 

 the cottonwoods, box elders and willows. Still farther 



