INTERPRETATION OF THE CURVE OF THE .SEQUOIA. 173 



caused me to carry the Asiatic curve lower than is justifiable. It is possible that there 

 really was a disagreement between Asia and America, but it is more probaljle that tlie 

 concentration of evidences of aridity in the way of abandoned ruins and the like at that 

 particular period led me to infer a pronounced minimum at a date when there was merely 

 a greater degree of ariditj' than hitherto, although not so great a degree as ensued within a 

 century or two. In general, as has already been said, the three noticeable depressions 

 in the Asiatic curve, namely, those in 300, G50, and 1200 a. d., are probably exaggerated, 

 because special events, due apparently to increasing aridity, happened to culminate at 

 about those dates. Yet each of the three comes at a time of increasing ariditj' in the 

 sequoia curve, and in the case of the minima of 650 and 1200 a. d. the sequoia curve is also 

 close to its lowest point. 



Returning now to our minute survej' of the curves, the maximum at 400 a. d. in the 

 Asiatic curve is wholly out of harmony with the California curve as it now stands. If, 

 however, the minimum of 300 a. d. is a mistake, the succeeding maximum becomes merely 

 a place where the descent of the curve is checked, just as in the tree curve. From 400 to 

 550 a. d. the curves agree. The maxima of 550 in Asia and 610 in California are probably 

 identical, although for reasons already explained the Asiatic curve drops too soon. In the 

 next section, from 600 a. d. to 1500 a. d., if allowance is made for the exaggeration of the 

 Asiatic minima, the two curves agree closely for 900 years. Here, as at the time of Christ, 

 the agreement is such that it can scarcely be a matter of chance. After 1500 the small 

 fluctuations agree to about the same degree as do the large ones for the preceding 2,000 

 years. The general trend of the American curve is upward, however, and that of the 

 Asiatic slightly downward. In this case the Asiatic curve is probably correct, for it is 

 based largely on recorded levels of the Caspian Sea. The American curve, on the other 

 hand, is probably wrong. This is the portion which is most seriously subject to errors due 

 to the flaring of the sequoias at the base of the trunk. A slight correction has been applied 

 for this, as already stated, but from the scarcity of young trees and from the general 

 agreement of California with other regions, it seems as if this correction should have been 

 greater. Probably the curve during the nineteenth century should be in the position 

 indicated by the fine dotted line in figures 50 and 54. 



The conclusions to be drawn from our two independent methods of investigating the 

 climate of the past may now be summed up. Three points stand out with especial clear- 

 ness. First and clearest, important climatic pulsations have apparently been in progress 

 throughout the historical period. They have a length of centuries, but do not show 

 any regular periodicity. They are often characterized by sudden changes of considerable 

 magnitude. The agreement of all our lines of evidence appears to establish the reahty of 

 the pulsations upon so firm a basis that there seems little likelihood that future work will 

 put it in question. Doubtless the details of our curves will be altered, but their sinuous 

 character with its indications of climatic pulsations is not likely to be destroyed. 



In the second place, climatic pulsations in western America and in similar latitudes in 

 western and central Asia are probably synchronous and of the same type. This conclusion 

 is by no means so firmly established as is the reality of the pulsations, but it possesses a 

 high degree of probability. In the 3,200 years covered by our two curves only the 200 

 years from 250 to 400 a. d. and 550 to 600 a. d. show positive disagreements which, if 

 confirmed, would militate against the conclusion just reached. During a much longer 

 period, about 800 years all told, the two curves show negative disagreements, not due like 

 the others to the direct interpretation or misinterpretation of actual facts, but to the 

 mere absence of data. Finally, for 2,200 years the two curves are in essential harmony so 

 far as their main fluctuations are concerned. Considering, then, the imperfections of the 

 Asiatic curve and the fact that the respects wherein it disagrees with the American curve 

 are those where it is known to be most liable to error, we may regard it as highly probal)le 



