PHYSIOGRAPHIC AND GEOLOGIC DEVELOPMENT 261 



fluvial and SBolian deposit is spread the next layer of mud, which 

 frequently is less extensive than the earlier deposits, thus giving 

 abundant opportunity for the observation of the exact manner of 

 burial of the older sand-covered stratum. 



Now while the alternations are as marked in Peru as in Chile, 

 it is noteworthy that the Tertiary material in Peru is not only 

 coarse throughout, even to the farthest limits of the piedmont, 

 but also that the alternating beds are thick. Moreover, there are 

 only the most feeble evidences of wind action in the lowermost 

 Tertiary series. I was prepared to find curled plates, wind-blown 

 sands, and muds and silts, but they are almost wholly absent. It 

 is, therefore, concluded that the dryness was far less extreme than 

 it is today and that full streams of great competency flowed vigor- 

 ously down from the mountains and carried their loads to the in- 

 ner border of the Coast Range and in places to the sea. 



The fact that the finer material is sandy, not clayey or silty, 

 that it almost equals in thickness the coarser layers, and that its 

 distribution appears to be co-extensive with the coarser, warrants 

 the conclusion that it too was deposited by competent streams of 

 a type far different from the withering streams associated with 

 piedmont deposits in a thoroughly arid climate like that of today. 

 Both in the second Tertiary series and on the present surface are 

 such clear examples of deposits made in a drier climate as to leave 

 little doubt that the earliest of the Tertiary strata of the Majes 

 Valley were deposited in a time of far greater rainfall than the 

 present. It is further concluded that there was increasing dry- 

 ness, as shown by hundreds of feet of wind-blown sand near the 

 top of the section. But the growing dryness was interrupted by 

 at least one period of greater precipitation. Since that time there 

 has been a return to the dry climate of a former epoch. 



Uplift and erosion of the earliest of the Tertiary deposits of 

 the Majes Valley is indicated in two ways: (1) by the deformed 

 character of the beds, and (2) by the ensuing coarse deposits 

 which were derived from the invigorated streams. Without 

 strong deformations it would not be possible to assign the in- 

 creased erosion so confidently to uplift; with the coarse deposits 



