ANCIENT LIFE HISTORY 



523 



mentary record of which is engraved upon certain of the 

 sedimentary rocks. Rocks which were formed under dif- 

 ferent conditions contain different species of life-forms, 

 showing that throughout all time the geographic condition 

 has had a marked influence upon plants and animals. 



The rocks and fossils also show that the geographical 

 conditions of certain areas have varied greatly. Some 



SKELETON OF AN ANCIENT AMERICAN ELEPHANT 

 Found near Los Angeles, California. 



regions have been below and above the sea several times. 

 Regions now cold have been warm, and those now dry have 

 been wet, and vice versa. Thus the life in certain areas has 

 suffered great changes by the geographical accidents to 

 which the region has been subjected. The petrified forests 

 near Holbrook, Arizona, show some of the most remarkable 

 tree fossils ever found and indicate that the region has been 

 subjected to remarkable geographical changes. 



