30 



University of California Publications in Geology [ VoL 11 



It is perfectly well known that marine organisms migrate with the seasons, 

 and that at a certain locality, where life was abundant during one season, it ia 

 almost entirely absent in another, the organisms having migrated into deeper 

 water. What is true of seasons is also true of longer periods, some regions for- 

 merly well stocked with organisms being barren for years at a time, after which 

 a return of the fauna takes place. Such migration up and down the ocean floor 

 is often determined by factors difficult to ascertain. In the Alaskan case it may 

 be due to the abundance of cold water carried in from the land by the melting of 

 the glaciers, which, as shown by Tarr, has recently become very marked through 

 changes which also caused an advance of the glaciers in certain localities. 



Later the same writer states : 



. . . absence of marine fossils is not an absolute indication of the non-marine 

 character of a formation, though absence over a very large area may probably be 

 taken as a fairly certain guide. 



It would seem, therefore, that the lack of fossils over a wide area, 

 and throughout great thicknesses, points very strongly to the conti- 

 nental deposition of the Franciscan sandstone. If the sandstone is 

 continental, one is inclined to wonder why no remains of land animals 

 have been found. Such remains may be present and it is possible 

 they have been overlooked, though it is not probable that they are 

 very numerous. 



Angularity of Grain 



The striking angularity of the clastic grains of the sandstone indi- 

 cates that the processes of transportation were not such as to produce 

 much rounding of grains. There could have been no great amount 

 of abrasion of grains either during transportation or deposition of 

 this material. 



Significance of Feldspar 



The presence of much feldspar has an important bearing on the 

 question of origin of this sandstone. The source of supply appears 

 to have been the granite of the Coast Ranges. 48 The mineralogical 

 composition of the sandstone shows that it was derived from granitic 

 rocks, and the angular nature of the grains indicates that they could 

 not have traveled very far. 



It is possible to imagine a granitic rock subjected to rock decay 

 in a temperate, humid climate where, due to the reworking of the 



48 It is, of course, possible that there was an uplifted area of granite on 

 the west side of the present Great Valley of California. This granite may have 

 been continuous with the granite of the Sierra Nevada. 



