4 TREE ANCESTORS 



These conclusions were all rational enough in their day, especially 

 when the belief was well nigh universal that the earth was only 

 about 6000 years old as estimated from the bibhcal chronicles. 

 When, however, it was finally reaHzed that nature had almost 

 h'mitless time at her disposal students began to perceive that the 

 apparently insignificant forces which we still find at work— the 

 action of air and water and vulcanism, and the slow changes 

 wrought by evolution, were the agencies that had accomplished 

 such tremendous results in past times. 



This belief in the uniformity of factors and the interpretation of 

 the past in terms of nature's forces that we find acting today was 

 christened uniformitarianism and the late Sir Charles Lyell (1797- 

 1875) may be regarded as the high priest of this beHef. It is quite 

 possible that the forces of nature may have apparently accomplished 

 more rapid results at certain times in the history of the earth but 

 it is very doubtful if, during the time when the ancestors of our 

 forest trees have flourished physical or organic history moved any 

 faster or by any different means than it moves today. 



This is one of the great principles of geology — that we may legit- 

 imately utilize present conditions in the interpretation of the 

 past, or in what Huxley called retrospective prophecy. We may 

 rest assured that boreal or temperate forests did not flourish in 

 proximity to tropical marine waters, and that insolation, humidity, 

 rainfall, and all the other factors of environment had effects on the 

 trees of past ages similar to their effects on the forests of today. It 

 is as unscientific to assume that trees did not react to their environ- 

 ment during the Eocene as they do at present as it would be to 

 assume that the carrying power of water was not conditioned 

 by its velocity during Eocene time. 



A second principle the enunciation of which will be helpful 

 throughout the subsequent discussions relates to cHmate. The 

 human race since its reached the stage of written traditions has 

 lived under chmatic conditions which in general are like those of 

 the present, with the familiar transition from torrid through tem- 

 perate to polar chmates in passing from the equator to the poles. 

 It is most difficult to think of past climates as in any way different 



