474 



THE CHANGING WORLD 



beginning and no prospect of an end," even before the " everlasting 

 hills " were born. The geological evidences of the passage of time are 

 plain and unmistakable to everyone. 



A visit to the Grand Canyon of the Colorado, for example, and an 

 inspection of the gigantic stone book there revealed, with its leaves 

 of stratified rock piled one upon another, must impress even the most 



flippant traveler with the 

 record of time spent that 

 is there displayed. Strati- 

 fied rocks made out of 

 sediment such as those 

 which form the walls of 

 that stupendous gorge 

 were built up first some- 

 what slowly through the 

 erosion of land masses, 

 then the sediment was 

 collected and borne away 

 by flowing streams and 

 finally deposited bit by 

 bit in horizontal beds 

 under water. These sedi- 

 ments were subsequently 

 compressed, cemented, 

 and hardened into layers 

 of stone, varying in thick- 

 ness. 



Sooner or later there 

 might follow the gradual 

 shifting of the levels of 

 land and water, possibly 

 caused by the aging and consequent wrinkling on a large scale of 

 the earth's crust. At any rate, whatever the cause, there has resulted 

 an eventual submergence here and there of what was once land, as 

 well as a slow up-thrust of the neighboring ocean bed to form newly 

 emerged land. 



Meanwhile rain fell, not continuously in delugelike floods, but 

 from time to time just as it does at present, with considerable intervals 

 between the rainy spells. In fact, there is every reason to believe 

 that all the processes leading to the formation of sedimentary rocks 



U. S. Geological Survey 



Erosion in the Grand Canyon of Colorado has 

 laid bare stratifications of soil formation de- 

 posited in centuries past. 



