420 i). WILLIS — SOME COAST MIGRATIONS, CALIFORNIA 



The sediments resulting from the erosion of that land have not been 

 discovered ; only the fact of a great hiatus in the record is obvious at 

 the unconformity. 



FRA NCISCA N H IST( ) RY 

 FRANCISCAN STRATIGRAM V 



The basal conglomerate of the Franciscan series is a very coarse shore 

 deposit composed of pebbles and boulders up to two or more feet in 

 diameter in a sandy matrix. The materials were derived from the»im- 

 mediately adjacent Coast complex upon which the conglomerate was 

 deposited. The strata exposed in the mountain slope are strikingly like 

 the deposits which constitute the beach at the base of the cliffs, and to 

 realize the aspects of the Franciscan coast the observer needs only to 

 consider those of the present coast. The Franciscan was a bold and 

 rocky shore, against which broke powerful waves (see plates 26 and 27). 



The stratigraphy of the Franciscan formation has not been ascertained 

 in any of its outcrops. It comprises several lithologic varieties with a 

 great range of character, from the coarse basal conglomerates to fine de- 

 posits, partly organic. The mass of the formation is sandstone and shale. 

 A minor portion consists of radiolarian chert and limestone. In the 

 section at Slate Springs the thickness exposed is, according to Fairbanks, 

 about 1,500 feet, and grades from the basal conglomerate westward and 

 upward into arenaceous black shales, with interbedded thin layers of 

 sandstone. 



FRANCISCAN GEOGRAPHIC CONDITIONS 



In the presence of the Pacific, one does not question that it was the 

 ocean whose waves wrought the Franciscan shore. The clip of the strata, 

 though nearly vertical, is toward the Pacific, and bears out the immediate 

 inference that it w r as the adjacent ocean in Franciscan time. Such was 

 probably the fact; but as in later epochs a water body existed east of 

 this position, apparently with a land area west of it, it should not be too 

 confidently assumed that this Franciscan shore was certainly the then 

 Pacific coast of the continent. It may have been the eastern coast of a 

 western land. 



NA TURE OF DEFORM A TION 



The structure of the Franciscan series is complex and among the 

 associated formations characteristic. Deformation has been accom- 

 plished chiefly by fracture, with minor folding. The shales are generally 

 plicated and broken at acute bends. The sandstones are broken and 

 faulted. The cherts are crushed. In man}' instances the sandstones 



