THE MIOCENE PERIOD 



809 



)merged. The Upper Miocene beds are therefore more .wide- 

 than the Lower. While clastic sediments predominate, 

 diatomaceous earths are still in evidence. 



Fig. 542. Fig. 543. 



Fig. 542. Map showing supposed distribution of land and water on the 



Pacific coast of the United States during the early Miocene period 



(Ralph Arnold.) 

 Fig. 543. Map showing supposed distribution of land and water on the 



Pacific coast of the United States during the late Miocene period. 



(Ralph Arnold.) 



The marine part of the Miocene system attains very notable 

 thickness, the Lower Miocene having a maximum thickness of 

 some 8,000 feet (Vaqueros 3,000, Monterey 5,000) and the Upper 

 Miocene hardly less. 



