8 



University of California. 



[Vol. 3. 



some of the genera of the new fauna, or, at any rate, a 

 suggestion of its general character has been expected to appear 

 below the physical break. 



It is probable that in time this great California orographic 

 disturbance will be definitely and reasonably correlated with the 

 marked epeirogenic (and locally slightly orogenic) uplift which 

 is conceded to have inaugurated Quaternary conditions in the 

 Eastern States. In that case, the Lafayette formation will be 

 recognized as the equivalent, in part at least, of the Upper 

 Pliocene of the Pacific Coast. If we base our determination of 

 the beginning of the Quaternary era in California on palaeon- 

 tological evidence, we would then have a longer era on this coast 

 than east of the Rocky Mountains, and more or less confusion 

 would result. On the whole, I think it more convenient, more 

 rational and therefore more scientific to place all the strata 

 which are structurally below the physical break, in the pre- 

 Quaternary periods, and that view will be adopted in the 

 following pages. 



In any case, the conclusions of this paper in the matter of 

 the probable length of the Quaternary era will not be seriously 

 affected; for the strata in dispute are thin and represent a very 

 short time in comparison with that of all of the Tertiary and 

 Quaternary eras. Indeed, it is rather remarkable that the 

 pala?ontological evidence based on the percentage of living 

 species in faunas should so nearly combine with the physio- 

 graphic evidence in establishing a natural and well-marked line 

 of division between the two eras. We can fix the line on this 

 coast much more satisfactorily than on the Atlantic Coast, as 

 in the latter region the supposed latest Pliocene strata, the 

 Lafayette formation, are lamentably barren of fossils. 



THE SIERRAN VALLEYS. 



Piru Creek rises in the high mountains west of the Upper 

 Pliocene basin near Gorman's Station and flows toward it, but 

 instead of following its old and apparently most natural course 

 across the area of soft rocks, it skirts the southwestern border, 

 keeping in the gneissic area and flowing in a deep canon. 

 Tributary streams have eroded broad, shallow valleys in the 



