210 CHANNEL ISLANDS OF CALIFORNIA 



were ever above the surface is difficult to tell. A 

 slight submergence of the California coast-line here 

 would make San Pedro Hill an island, while a mini- 

 mum elevation of one hundred and seventy-five feet of 

 the coast-line, according to Smith, would make Tanner, 

 Cortez, and Osborne Banks islands. 



In ages past, and by this is meant miUions of years 

 ago, all this region was pushed up and depressed time 

 and again. The terraces of San Clemente are marvellous 

 pages in the diary of the ages, showing beach after 

 beach raised into the air. With this, possibly, came 

 Tanner and Cortez, until they rose above the surface, 

 only to be beaten down and blown and washed away. 



Regarding the banks of Tanner, Cortez, and Osborne, 

 Dr. W. S. T. Smith, in his "Topographic Study of the 

 Islands of Southern California," frequently referred 

 to in this volume, says : 



"As shown by the soundings, these banks exhibit character 

 identical with those of the upper submerged platform. They 

 are more or less platform-Hke in character, and at an average 

 depth corresponding to that of the submarine platform, and 

 the descent beyond the six-hundred-foot contour is generally 

 rapid. There can be little doubt, therefore, that these banks 

 were islands only a short time ago, geographically speaking, 

 and that they have been completely truncated by wave action 

 during the most recent stages of marine abrasion." 



