172 



THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



150() 



Bearing in mind, then, the limitations of the Asiatic cm-ve, let us compare it with the 

 main features of its fellow from California. At the beginning the two curves take a sudden 

 drop in close harmony, a rather remarkalile coincidence, but one that must not be much 

 emphasized, since the California curve is based on a single tree and the Asiatic curve on 

 the evidence of a few famines and an uncommon degree of movement among the peoples 

 of the lands around the eastern Mediterranean. Next we get pronounced disagreement, 



1400 1600 1800 2000 



Fig. 50.— Changes of Climate in California ( ) and western Asia ( ) during Historic Times. 



but this is less significant than the pervious agreement. It may be due simply to absence 

 of data in compiling the Asiatic curve. Between 1200 and 950 b. c. no climatic data 

 whatever had come to light in Asia when the curve was drawn; hence these two points were 

 connected by a straight line. If our information had been fuller we might have been led 

 to draw a curve similar to that of the sequoias, although less exaggerated. At 950 b. c. 

 both curves show a decided maximum. Then for 250 or 275 years they swing downward 

 and again upward, smoothly in one case and with many minor variations in the other, and 

 reach maxima at 690 and 660 b. c, respectively. Considering the fact that the tree curve 

 is much exaggerated because this portion is founded on so few trees, while the other curve 

 is based on very scanty historical data, the agreement may be considered close. Next, 

 both curves drop to a minimum in 600 b. c, after which the trees rise to a marked maximum 

 in 400 B. c, while the Asiatic curve rises only a little and has no corresponding maximum. 

 Here, once more, we have a distinct disagreement. It is more significant than that of the 

 twelfth century b. c. because it comes later when the number of trees is larger and historical 

 records more numerous than six centuries before, but it is of the same general type. In the 

 period from 600 b. c. to 300 b. c. the Asiatic curve is drawn as a straight hne because of the 

 absence of any positive data during that long interval. If further information were at 

 hand the Asiatic curve would undoubtedly be sinuous, and the few scraps of evidence 

 available indicate that it quite certainly would not be low at 400 b. c. and probably would 

 be high. The next maximum comes at 300 b. c. in one curve and 280 in the other, a good 

 agreement. The succeeding minima culminate nearly 100 years apart, but here again 

 the basis of the Asiatic curve is merely evidence of heavy precipitation about 300 b. c. 

 and of low precipitation 150 years later. There is nothing to show how far the curve 

 should depart from a straight line or the exact point where it should be at a minimum. 

 Here, then, as in the twelfth century a. c. and at 400 b. c. the two curves disagree, but 

 the disagreement is of a purelv negative character and hence of no great significance. 

 For the next 380 years, from about 130 b. c. to 250 a. d., the curves agree to a remarkable 

 extent. Then comes a disagreement, the first which is genuinely positive and hence 

 significant. The pronounced Asiatic minimum at 300 a. d. indicates one of two things. 

 Either the climate of Asia at that time suffered a change which did not affect California, 

 or else a distinct mistake has been made in the Asiatic curve. In view of the close agree- 

 ment of other portions of the curve I am inclined to the second supposition. The fact that 

 indications of aridity happened to be especially well preserved at the time has probably 



