THE ROMANCE OF OUR TREES 



vast changes in the earth's surface. Its close was 

 marked by a period of great cold which wrought 

 havoc among vegetation, and to-day much land that 

 in Tertiary times was forested is hidden under enor- 

 mous ice-fields. In Tertiary times most of the 

 present Arctic Zone was probably free of ice, at any 

 rate Spitzbergen, Greenland, Iceland, the extreme 

 north of the mainland of America and Asia enjoyed a 

 climate at least as mild as New England does to-day. 

 Vast forests circled the whole of to-day's Arctic 

 regions, for the land connection was complete. In 

 those times the types of tree vegetation were similar 

 throughout the whole Northern Hemisphere. Doubt- 

 less, then as now, species had a limited distribution, 

 but the genera then, much more so than to-day, were 

 widespread. Tulip-trees, Magnolias, Sweet-gums, 

 Ginkgos, Sassafras, Sequoias, and, indeed, countless 

 others grew in Europe, in America, and in Asia. 



As the period of great cold came on so the vegeta- 

 tion was forced to migrate down the mountains and 

 southward to escape destruction. As the ice crept 

 southward so it destroyed the vegetation. The 

 trees of Greenland, Spitzbergen, Iceland, of the re- 

 gions separating North America and eastern Asia, 

 were all destroyed. In this country they were forced 

 south of Philadelphia (Lat. 40° N.) and where there 

 was no continuous land connection they were oblit- 



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