Hershey.] 



Quaternary of Southern California. 



7 



as determined by Turner.* It is evident that the territory of 

 California at a time closely following on the deposition of the 

 recognized Upper Pliocene marine deposits was the site of a 

 profound orographic disturbance which radically modified its 

 surface conditions. The wide extent and great importance 

 of this disturbance have recently been recognized by other 

 investigators.! It properly terminated the Pliocene history and 

 inaugurated typical Quaternary conditions, so that it is perfectly 

 natural to consider it the opening event of the Quaternary era 

 in the State of California. 



I am informed that palaeontologists (including Arnold) are 

 finding a typical Pleistocene marine fauna in the upper portion 

 of the Merced series and its Southern California equivalent, a 

 series the greater portion of which is by common consent 

 considered Upper Pliocene in age; and by them it is proposed 

 to place the inferior boundary of the Quaternary era chrono- 

 logically below the great orographic disturbance outlined above, 

 a proposition to which I most vigorously demur. The line 

 dividing the Pliocene and Pleistocene should be so drawn as 

 to be of the greatest convenience to the greatest number of 

 geologists. If the line is placed in the conformable strata below 

 the physical break, it can only be recognized in a few limited 

 basins, but if the great orographic disturbance which suspended 

 deposition in those basins be accepted as the first Quaternary 

 event, no difficulty will be experienced in properly placing it 

 throughout the State. At most, there can be no great difference 

 between a late Pliocene and an early Quaternary fauna. A 

 mere shifting of ocean currents might bring about the change 

 observed. It would be too insignificant an event to counter- 

 balance the radical change in physical conditions which must 

 have resulted from the upthrust of the California mountains. 

 The latter has by far the greater right to fix the limit of the 

 Tertiary era. It has been customary for many years to place the 

 division between eras in chronological positions corresponding 

 to non-conformities among the strata and the introduction of 



*Bull. Geol. Soc. Amer., vol. II, p. 402. 



tThe Physiography of California, by Dr. H. W. Fairbanks; Bull. Amer. Bur. 

 Geog., vol. 11, Sept. and Dec, 1901. 



