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sea on the west coast of North America. Here in latitude 

 40 to 45 degrees, the geologist finds types of topography 

 built up or shaped by ice action, yet so modified and 

 buried beneath successive growths of conifers that only 

 the trained eye of the close observer can follow the forms 

 and features. In the next few degrees northward, the 

 work of the glacier is less modified and hence more dis- 

 tinct. Great forests tower over and grow upon successive 

 generations of fallen trees, which rest upon glacial 

 debris. Still further north, and at the same general 

 elevations above the sea, these forests grow upon a 

 thinner layer of dead and rotting trunks and the 

 humus is less thick. Still more northward yet, these 

 forest trees are found in the prime and vigor of full 

 growth — no aged and fallen trunks encumber the ground, 

 the roots of the living trees are buried in the gravelly, 

 rocky soil of moraines and a thin layer of decomposing 

 vegetable matter covers the ground. Where there is no 

 morainic material, the thin soil' gives scant roothold, 

 and an upturned root sometimes uncovers fresh glacial 

 scratches. From commanding positions, the glittering 

 glacier can be seen, and as he nears its front, the ob- 

 server is forced to note that the forests are of young and 

 half grown trees, then saplings and finally the very seed- 

 lings sprout from the freshly uncovered gravel of the 

 matchless glaciers of British Columbia and Alaska. 



Now and then these young forests are uprooted and 

 plowed under by a temporary advance of the glacier, 

 and its gradual retreat will sometimes reveal the crushed 

 roots and trunks of a previous advance. But the inte- 

 gral of successive retreats is greater than the integral of 

 successive advances, and the forest has for thousands of 

 years kept an accurate record of the fact, although suc- 

 cessive generations of dead trunks, whose decay has 



