SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. 83 



shows the work of the Teredos or aUied genera ; and the shal- 

 lowness of the water is shown by the fossil remains, or casts, 

 of Fucoids and other marine plants. 



After this elevation of the western portion of the continent, 

 and the formation of the Coast Range, by folding of the strata, 

 and subsequent to a period of erosion, the entire region was 

 again submerged, and the eroded summits of the mountains of 

 Cretaceous and Eocene (older Tertiary) sedimentary forma- 

 tions were buried under several thousand feet of sediment at 

 the bottom of the Miocene sea. 



This later formation consists of sandstone, light-colored, 

 banded slates, and gypsum-bearing clays. 



(Some of the results of this submersion may be seen in 

 the Miocene capping the present mountain ranges. In some 

 instances the horizontal strata of Miocene age may be seen cap- 

 ping the nearly vertical strata of the later Cretaceous or Eocene 

 rocks at altitudes of about five thousand feet.) 



While the former elevation drained the Cretaceous sea of 

 the region, the submergence following it allowed .the Miocene 

 sea to occupy the place of the former Cretaceous, the elevation 

 of the Miocene period raised barriers which formed an inland 

 sea which continued during a part of the Pliocene period. 



After this came a series of elevating and sinking move- 

 ments in the region. The Pliocene sea broke through the bar- 

 riers and was drained into the Pacific Ocean, and the present 

 interior valleys were occupied by fresh-water lakes, and still 

 later by the bodies of salt water now occupying the so-called 

 "Bay Region" of Central .'California. 



Referring again to the Post-Cretaceous period, we find 

 that the reniarkable changes in the physical geography of the 

 earth's crust resulted in corresponding climatic variations. 



These culminated in a revolution in the organic life of the 

 time, which was perhaps the greatest which has occurred in the 

 world's history. 



The evidences of these great surface alterations are seen in 

 the almost universal unconformity of the rocks of the Tertiary 

 strata with those of the Cretaceous and other periods which 

 preceded it. 



The unconformities and breaks in the record characterizing 

 this critical period are almost universal throughout the world, 

 the most notable exceptions being the plateau region of the 

 North American continent, and some portions of California, 

 where the crust oscillations appear to be less marked, and the 

 stratification is doubtfully continuous. 



The next critical period occurred at the close of the Ter- 

 tiary, when another great revolution took place which re- 

 sulted in the destruction of a large part of the organic life of 



