156 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



This involves anticipation of two conclusions which are to be discussed in the following 

 chapter: first, that the sinuosities of the sequoia curve actually represent pulsations be- 

 tween aridity and moisture ; second, that the pulsations in California have been essentially 

 synchronous with those of Central Asia. 



Assuming for tlie present that these two conclusions are valid, we may correct the 

 curve of the sequoia. For this purpose, the following critical levels of the Caspian Sea 

 have been taken as the standard : 



Mean level 1750-1S90 a. d. equals feet. 



Recorded high level in 920 A. D. equals +29 feet. 



Estimated level below ruins now under water, in seventh eentury, —20 feet. 



Estimated level about the time of Christ +85 feet. 



Estimated level about the time of Herodotus +150 feet. 



The historic and phj'siographic evidence in sui)port of these figures is given in the 

 chapter of "The Pulse of Asia" already referred to. On the basis of these levels of the 

 Caspian Sea the curve of the sequoias has been tilted in such a way that the portions at 

 the respective dates given above lie at heights approximately proportional to the height of 

 the Caspian Sea at the corresponding dates. Further than this no change has been made. 

 In applying this "Caspian corrective factor," the sequoia curve has been divided into 

 four portions: (1) from the earliest times until 400 b. c, a portion which has simply been 

 raised to correspond with the inferred level of the Caspian at 400 b. c. but has not been 

 tilted because we have no knowledge of the sea in earlier times; (2) 400 B. c. to 400 A. D., 

 which has been tilted in such a way that 400 b. c. hes 15 per cent higher than in the curve 

 of figure 38, while 400 A. d. is unchanged; (3) 400 A. d. to 900 A. D., which is unchanged, 

 and (4) 900 A. d. to the present time, which has been tilted so that the modern end of the 

 curve lies 9 per cent lower than in figure 38. In addition to this I have arbitrarily made a 

 slight reduction in the great maximum which cuhninates about 1000 b. c, but this is a 

 matter of no importance. The exact extent to which the position of the curve has been 

 altered in each decade is indicated in the column headed "Caspian Corrective Factor" 

 in Table G, pages 323-324. 



The resultant curve, given in figure 50 on page 172, represents the nearest approxi- 

 mation that now seems possible to the actual curve of growth of the sequoias as it would 

 be if it were uninfluenced by differences in the rate of growth of old trees and young, or 

 by any other influences except those of climate. Its fiu'ther discussion will be deferred 

 imtil we have considered the reasons for beUeving that the low portions indicate aridity, 

 while the high indicate abundant moisture ; but one vital point must again be emphasized : 

 it may seem, perhaps, that we have taken liberties with our curve of growth and have 

 altered it arbitrarily; but this is far from the case. Every alteration has been based on 

 strictly mathematical considerations, and no assumptions have been made except at the 

 very end, where the Caspian factor is used. Even so, nothing has been done to alter the 

 location of the sinuosities of the curve. A comparison of the dotted line of figure 38 and 

 the solid line of figure 50 shows that although many corrections have been applied, the 

 essential features, that is, the ujjs and downs which appear to indicate climatic pulsations, 

 have not been essentially changed either in position or in relative imjjortance. 



