302 



THE POPULAR SCIENCE MONTHLY 



The fossil trees exposed at this point are along the upper slope 

 of the southern wall of Lamar Valley. The slope here makes an 

 angle of about thirty-three degrees with the horizon, and is about 

 nine hundred feet long. The petrifactions are standing all the 

 way up this slope, interspersed with the living conifers of to-day, 

 represented at Fig. 1. At first sight it appears that either these 

 ancient trees grew upon the slope now exposed, and that there had 

 been no change in the slope from that day to this, or that the 

 present had brought back exactly the same surface conditions as 

 existed when the now silicified trees were alive. Such an appar- 

 ently simple conclusion would, however, involve more remarkable 

 phenomena than are yielded by the true explanation. 



A little consideration, taken in connection with the formation 

 of the bluffs that connect Lamar Valley with the higher lands to 



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f Ancient Forest Trees. I Petrified Remains. 



Fig. 2 



Living Trees. 



the south and west, shows clearly the action that has placed the 

 living and petrified trees upon the same slope at this and at many 

 other points in the region. 



A series of forests has grown upon successive levels, each 

 level having been produced by an accumulation of volcanic mate- 

 rial which destroyed the then existing forest. This explanation 

 will be readily understood from Fig. 2. The level upon which the 

 first forest grew is indicated by 1. The level of the volcanic 

 accumulation which destroyed this growth of trees is shown at 2. 

 Upon this second level came another growth of trees, which in 

 turn was destroyed by the accumulation extending to the level 3. 

 Still another forest grew upon 3, which in course of time was 

 destroyed. This alternate growth and destruction was repeated 



