EFFECT OF CLIMATIC CHANGES ON GLACIATION 563 



remarkable series of strands in the Searles Valley, 22 in all, including 

 the overflow strand, is most extraordinary. After this lake ceased to 

 overflow it was for a long time the end member of the Owens Lake series. 

 It received its water from a long, narrow, structural valley surrounded 

 by mountains, which in some places rise 9,000 feet above its floor. It 

 thus forms one of the best rain-gauges in America. The topographic 

 relationships are such that each little variation in climate is recorded. 

 Free suggests that the *'very faint strands eighteen inches to two feet 

 apart" in the lower 200 feet of the terrace series may "represent annual 

 stages in the retreat of the ancient lakes." It seems more probable that 

 they represent longer periods, such as the sun-spot cycle, or the 21-year 

 cycle of Douglass and the 35-year cycle of Briickner. If this is so, the 

 larger strands would represent periods from a few hundred to a thousand 

 years in length, such as appear in the main fluctuations of the curves of 

 tree growth in California. It is worth noting that the western edge of 

 the Owens Valley drainage area is only from 25 to 35 miles from the dis- 

 tricts where the big trees were measured. The general climatic fluctua- 

 tions must be similar. A series of twenty or thirty cycles, such as those 

 which are shown by the trees to have culminated in the fourteenth, tenth, 

 and first centuries of our era, would bridge the gap between the last Gla- 

 cial period and the present day. That the strands preserve a remarkably 

 full record of the events which occurred during this interval seems highly 

 probable. Whether the level of Lake Searles fell greatly after each strand 

 was formed and then rose again to form the next lower strand, or whether 

 it merely fell and then paused, can not yet be determined. In either case 

 the interval between the Glacial period and the present time seems to 

 have been filled with constant climatic pulsations whose general tendency 

 has been toward less and less severity. The complexity of the changes 

 indicates that we must appeal to some highly variable cause, such as the 

 sun, rather than to causes, such as crustal deformation and changes in 

 the composition of the atmosphere, which by their very nature act slowly 

 and do not repeatedly reverse themselves at short intervals. The absence 

 of any gap between the past and the present suggests that the same cause 

 has been constantly operating. 



THE INCLOSED LAKES OF ASIA 



The lakes of the Old World furnish the same kind of evidence as those 

 of the New. The fluctuations of the Caspian seem to be of the same sort 

 as those of other lakes all the way from North Africa^^ to Mongolia.^^ 



" See H. J. L. Beadnell : A desert oasis, pp. 110-122. 

 18 D. Carruthers : Unknown Mongolia, vol 2. Appendix. 



