70 Adventures in Scenery 



sediments into which the granite magma forced its way, and for 

 the exposure over large areas of nearly uniform granite rocks. 

 The character of the formations of the Franciscan group in- 

 dicates a migration to and fro of the shore-line of the Franciscan 

 sea. Limestones and cherts were deposited on sea floors far from 

 shore, whereas sandstones are clearly littoral or beach deposits. 

 The migration of the shore-line indicated by the alternation of 

 sandstone with either limestone or chert means a vertical move- 

 ment of the land in respect to sea level. In the Franciscan group 

 of formations there are three deep sea deposits that are separated 

 by rocks formed of coarser material, and sand, which indicates 

 three notable depressions of the region in Franciscan time, and 

 three movements of uplift. Thick deposits of sandstone means 

 sinking sea bottom, the floor of the ocean slowly subsiding and 

 the sands continuing to be deposited as the bottom sank. Con- 

 glomerates indicate shore deposits, as the pebbles sink before 

 being carried far out from shore. The coarse pebbles of a con- 

 glomerate formation generally mean erosion by streams having 

 rapid currents coming from higher lands near by. At Slate 

 Springs, on the coast of Monterey County, the basal conglom- 

 erates and sandstones are fully 1,000 feet thick. The sandstones 

 of the Franciscan formation are usually thick-bedded. The 

 outcrop of sandstones, together with thin beds of shale and 

 lenses of jasper, on the coast of San Luis Obispo Bay, near Port 

 Hanford, show a vertical section of approximately 10,000 feet, 

 or nearly two miles. Such a vast thickness of sandstones means 

 that the sea bottom progressively sank as the sands accumulated. 

 Coarse sandstones and conglomerates are usually spread over a 

 sinking continental slope by a transgressing sea. The jasper 

 beds, like shale, represent deep-sea conditions. The rock is made 

 up of minute skeletons of microscopically small animals such 

 as inhabit only deep water. The occurrence of beds of jasper 

 rock in the widespread sandstone formation indicates abrupt 

 change in the conditions of the ocean bottom as to depth and 

 distance from shore. 



