72 AN INTRODUCnON TO THE STUDY OF FOSSILS 



Fig. 25. — An ideal section through the fossil forests of Amethyst Mountain, in 

 the Yellowstone National Park. There occur in this region 2000 feet of volcanic 

 material in layers alternating with at least fifteen successive forests, indicating 

 thus fifteen volcanic outbursts separated by at least sufficient time to allow the 

 growth of forest trees with a diameter of two to ten feet. (From Holmes.) 



