INTERPRETATION OF THE CURVE OF THE SEQUOIA. 171 



such severity as during the fo'st part of the winter, for they are soon affected by the coming 

 on of the conditions which prevail in summer when the winds are weaker than in winter. 

 AVlien winters of this type prevail in California, the ordinary California type is pushed 

 farther south. At such times regions Uke southern Arizona would probably get as many 

 storms as Utah now gets, while places as remote as the Gulf of Mexico would be visited 

 by frequent "northers." 



Meanwhile our general conclusion may be sunamed up thus: Judging from what we 

 have seen of the rainfall of to-day and of its relation to the growth of the sequoias, high 

 portions of their curve seem to indicate periods when the winters were longer than now, when 

 storms began earlier in the fall and lasted later into the spring, and when mid-winter was 

 characterized by the great development of a cold, continental, high-pressure area, which 

 pushed the storms of the zone of prevaUing westerly winds far down into subtropical regions 

 and thus caused subtropical conditions to invade what is now the zone of equatorial rains. 



With this interpretation of the curve of the sequoias before us, we are prepared to 

 consider its meaning in reference to the history of the world as a whole. Figure 50 shows a 

 dotted line representing the approximate cUmatic fluctuations of historic times as given 

 diagrammatically on pages 327 and 403 of "Palestine and its Transformation." Leaving 

 out of account the slope of the sequoia curve to correspond with the changes in level of 

 the Caspian Sea, let us see to what extent these two entirely independent curves of tree 

 growth in CaUfornia and of chmatic pulsations in Asia agree. The number of maxima 

 in the Asiatic curve is far less than in the one from CaUfornia, but this is of no special 

 significance. By its very nature the Asiatic curve is a mere approximation and can not 

 be expected to show minute details. The evidence on which it is based, especially in 

 the early portions, is so scanty that long gaps, sometimes 100 or 200 years in length, 

 may intervene between two points for which data are available. In such cases the method 

 adopted was to draw a straight line between the points regardless of the fact that fluctu- 

 ations of much importance may have taken place in the interval. Moreover, even though 

 the Asiatic lines of evidence point to exceptional aridity or moisture, we can not in most 

 cases be sure that they indicate the dates when those conditions reached a maximum. 

 For example, we find evidence of aridity both before and after 1200 a. d., while moist con- 

 ditions are indicated in 1000 a. d. and 1325 a. d., but we can not be sure that these are 

 exactly the times of the true maxima and minima of rainfall, nor can we be certain as to 

 whether the dry periods or the moist periods were more prolonged. Hence it is a pure 

 matter of personal judgment whether we shall draw a U-shaped or a V-shaped curve. 

 In addition to all this it has thus far been generally impossible to determine how low a 

 given depression should faU. For example, at 300 a. d., 650 a. d., and 1200 a. d. evidences 

 of increasing aridity are especially noticeable; hence the curve drops deeply. Yet so far 

 as the actual facts are concerned the lines might have been drawn as indicated by the 

 dashes. Finally, although the writer was not at the time conscious of it, the exact form 

 of the Asiatic curve was determined in some respects by a preconceived idea which now 

 appears to be erroneous. The idea was that changes of climate must be gradual and that 

 lines with sharp angles and sudden risings or fallings could not possibly represent the facts. 

 This, for example, prevented the maximum in the sixth centurj' from being placed as late 

 as certain ruins would suggest. Inasmuch as everything pointed to extreme aridity 

 about 625 a. d., it was supposed that the change toward that aridity must have begun at 

 least half a century or more prior to that time ; it was not realized that a moderate change 

 might occur suddenly when conditions were already none too favorable, and might produce 

 the same results as a greater change acting less rapidly. Taking the Asiatic curve as a 

 whole, then, we must bear in mind that it is only a preliminary sketch, a pioneer attempt 

 to elucidate a most complex subject, and that the necessity for visuaHzing our conclusions 

 in the form of a curve compelled the making of a large number of more or less important 

 assumptions. 



