The San Francisco Earthquake 



285 



larger islands in the bay, it contains also 

 some of the most interesting and charac- 

 teristic rocks of the western coast, such 

 as the serpentines, the blue g'laucophane 

 schists, with their wonderful miner- 

 alogical variety, and peculiar jaspery 

 rocks made up in part of the siliceous 

 skeletons of radiolaria. The age of the 

 Franciscan series, which forms a large 

 part of the Coast Range, is still open to 

 question. It is thought by some geolo- 

 gists to be Jurassic, by others to be early 

 Cretaceous. 



The deposition of the Franciscan sedi- 

 ments was ended by an upward move- 

 ment of the sea bottom. They were 

 folded and faulted, lifted above sea-level 

 and eroded by streams and waves. Again, 

 however, the land went down, the Fran- 

 ciscan rocks sank beneath the sea and 

 were covered by thousands of feet of 

 fossiliferous Cretaceous, Eocene, and 

 Miocene deposits. The sediments of the 

 last period alone attained a thickness of 

 over 8,000 feet. At the close of the 

 Miocene and after minor oscillations of 

 level the rocks were again raised above 

 sea-level and were crumpled and faulted 

 by the energy of the uplift until they 

 formed a well-defined range separating 

 the ocean from the interior valley. 



In Pliocene time the land again sub- 

 sided, although the Coast Range was 

 probably not wholly submerged, and 

 marine deposits of this period were laid 

 down in sounds or inlets. 



I [ere belongs the San Pablo formation, 

 a thick accumulation of sandstones with 

 intercalated volcanic tuffs. Apparently 

 during the later stages of San Pablo dep- 

 osition new movements of the land took 

 place whereby fresh- water basins were 

 formed, in which accumulated over 3,000 

 feet of sediments and lava flows — the 

 Berkleyan and Campan series of Profes- 

 sor I. aw son. Nor is this all. Still later 

 in the Pliocene was deposited the Merced 

 series, which is exposed along the ocean 

 beach west of San Francisco. This re- 

 markable deposit, described and named 

 by Professor Law son, is a mile in thick- 

 ness and has at its base the well-preserved 



remnants of a coniferous forest. Thus a 

 portion of the Tertiary land upon which 

 pines, indistinguishable from the species 

 were growing now common at Monterey, 

 sank beneath waves to a depth of at least 

 5,000 feet, and so rapidly that the trees 

 were buried under sediments before they 

 could decay. Finally the Merced series, 

 carrying in its upper beds fossils of 

 Quaternary age — the mere yesterday of 

 geological time — have been elevated 

 above sea, tilted up at angles as high as 

 75 degrees, and dislocated by a fault of at 

 least 7,000 feet throw. 



THE COAST RANGE COMPARED TO THE 



ATLANTIC SEABOARD' 



In order that the full significance of 

 this epitome of the marvelous history of 

 the Coast Range may be appreciated, let 

 us turn for a moment to the Atlantic sea- 

 board. Here the entire series of post- 

 Jurassic rocks constitutes a compara- 

 tively thin veneer upon a coastal plain 

 that nowhere rises more than a few 

 hundred feet above the sea. The sedi- 

 ments are in large part unconsolidated, 

 are practically horizontal, and are ex- 

 Dosed only in the low banks of streams 

 that flow sluggishly across the plain from 

 the crystalline piedmont belt to the sea. 

 On the Pacific coast, on the other hand, 

 rocks of the same age have a thickness 

 that may easily exceed 40,000 feet, have 

 been deposited under conditions involv- 

 ing repeated vertical oscillations of the 

 land measurable in thousands of feet, 

 and have been folded and faulted into 

 mountain ridges now standing thousands 

 of feet above the ocean. Most significant 

 of all is the fact, already brought out but 

 presently to be further emphasized, that 

 this extraordinary geological activity has 

 continued up to the very dawn of the 

 human era and is probably still in opera- 

 tion. 



"faulting" 



If any one will look at a good map of 

 California he can scarcely fail to notice the 

 striking parallelism of structure shown 

 by that part of the state lying north of 



