The Geological Story Briefly Told 69 



all sedimentary formations in the central Coast Ranges between 

 the basement complex of granites, schists, and marbles and the 

 formations of the Franciscan group is evidence that a land area 

 existed in the region during the long Palaeozoic era, till the 

 ushering in of the Jurassic seas, when the sediments of the Fran- 

 ciscan period were deposited. 



The high mountain chain which had been formed in the 

 region of the Coast Ranges by the earth disturbances that culmi- 

 nated in the intrusion of granitic rocks in early Jurassic time was 

 subjected to long-continued erosion and was greatly degraded 

 before the subsidence which brought in a great arm of the ocean 

 and the deposition of the Franciscan sediments. Toward the 

 close of Jurassic time the sea encroached upon the land, and the 

 Franciscan sediments began to be deposited over the deeply 

 eroded surface of the crystalline complex. Wherever the base 

 of the Franciscan sediments is exposed by erosion it is seen resting 

 upon these granitic rocks in the form of a thick basal con- 

 glomerate or of sandstone. 



The Franciscan group occurs extensively in the Coast 

 Ranges. This encroachment of the sea upon the land extended 

 northward as far as the region of the Klamath Mountains and 

 southward as far as eastern Monterey County. Farther south 

 the sediments of this period pass under the Cretaceous and other 

 younger formations. No formation is known between the 

 Franciscan and the crystalline basement complex. The latter 

 then must represent the ancient land over which the sea gradu- 

 ally crept as the Franciscan sediments were deposited. The 

 absence of all sedimentary formations in the central Coast 

 Ranges between the basement complex of granites, schists, and 

 marbles and the various members of the Franciscan group is 

 convincing evidence that an extensive land area existed in the 

 region during a long time, an interval sufficiently long for the 

 removal through the whole of the Coast Ranges of the ancient 



