AND ITS INHABITANTS 185 



everywhere dot the country from Mongolia through Turkestan 

 and Persia to Turkey and North Africa, and also in our own 

 Southwest. In the deserts, roads too dry for caravans, but 

 known once to have been much used, also point to a change in 

 rainfall. So^ too, do abandoned springs and the scanty supply 

 of water in many aqueducts. One of the most significant pieces 

 of evidence is the amount of salt dissolved in the waters of 

 Owens Lake in southern California, and of Pyramid and Win- 

 nemucka lakes in Nevada. This, as Gale has shown, indicates 

 that from 2,000 to 4,000 years ago these lakes must have been 

 so high that they overflowed and were fresh. About 2,000 or 

 2,500 years ago Owens Lake appears to have been two and 

 one-half times as large as now and to have stood 180 feet 

 above Its present level. 



It is not enough to conclude merely that the climate of the 

 present is different from that which prevailed 2,000 or 3,000 

 years ago. We must know the nature of the change. Geolo- 

 gists formerly thought that climatic changes proceed very 

 slowly and uniformly in one direction. They now believe 

 that they are highly irregular. Even when the general change 

 during thousands of years is decidedly in one direction, it is 

 marked by great irregularities. There is now a general con- 

 viction that the same is true of historic times. Pulsatory 

 changes have apparently occurred whereby certain centuries 

 have been moister than the present and others drier. No 

 other hypothesis seems adequate to explain the fact that lakes 

 whose waters are known to have stood many feet above their 

 present level also contain ruins buried beneath their waters. 

 Equally strong evidence is afforded by the fact that the growth 

 of the big trees of California indicates constant pulsations 

 whose main features agree with those inferred from other 

 kinds of evidence in Mediterranean regions and central Asia. 

 In our own day exact records show an unmistakable harmony 

 between spring rainfall and tree growth In California on the 



