246 



Adventures in Scenery 



tion picture erosion of the land as going on till the uplifted 

 region was again reduced to a low flat plain with streams mean- 

 dering widely over the worn-down surface. 



Submergence and Uplift Repeated, and 

 Final Uplift of Present Range 



Again the sea covered the land as a new geologic epoch was 

 ushered in. When an eroded land surface is covered by the sea 

 and deposits are thrown down upon the more or less broken 



Photo by W. C. MenJenhall, U. S. Geol. Survey 



FIG. 73. Coastal Bluffs, Santa Monica. View west from near mouth of 

 Santa Monica Canyon. 



former land surface the new formation deposited by the later 

 sea does not "fit" upon the old eroded surface, and the result 

 is an "unconformity." It thus comes about that the Modelo 

 formation, which rests upon the earlier formed Topanga for- 

 mation, is separated from the latter by the broken line of the 

 old land surface. The Modelo formation is made up of the 

 remains of great numbers of minute organisms known as dia- 

 toms, which swarmed in the sea; of volcanic ash thrown out 



