THE FORESTS OF LONG AGO 43 



their coming brought profound changes to all forest life. They 

 invaded the land and as the centuries passed they have gradu- 

 ally taken possession of the world's most favorable portions, 

 forcing the pine and spruce and the fir back until they occupy 

 now the less fertile places, the high mountainous countries, 

 the dry sandy soils, and the desert's edge. 



In a sense the world has become and still is an immense 

 battle-field between the cone-bearers and the trees with broad 

 leaves. Gradually the cone-bearers are losing and being forced 

 out. During those times of the broad-leaf trees first invasions 

 lived a few trees that exist in our forest today the sequoia, the 

 bald cypress, and the ghinko. The rest the thousands of others 

 have perished and been replaced by more recent species. 

 Meanwhile the Rockies were being pushed up into existence 

 bringing about important changes in climate, for when that 

 tremendous barrier cut off the moisture-laden winds from the 

 Pacific, the country just east of them became too dry for tree 

 growth and so the plains country came into being. 



But this long period of warmth when the fig and the palm 

 grew far to the north and when tropical forests flourished in 

 Alaska did not last. It was followed by a glacial period, an age 

 of ice. A great ice cap moved down out of the north, forcing 

 both animal and plant life before it, grinding everything in its 

 way to extinction. We believe there were four distant ice inva- 

 sions and between each the climate was about as we know it 

 today. 



This ice sheet was a tremendous modifier of tree species. 

 Some species were able to keep ahead of the ice, for their seeds 

 borne by the winds or carried by rivers, birds, or animals were 

 scattered to the south of the ice flow and so the species was 



