174 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



that the main climatic pulsations of the temperate portions of central and western Asia 

 agree with those of the same latitude in western America. If these two regions, 10,000 

 miles apart, thus agree, it seems probable that in regions Ijdng in the same latitude and 

 having the same seasonal distribution of rainfall, similar changes must have taken place 

 all around the globe, or at least over all the continents, while corresponding, although not 

 necessarily similar, changes must have occurred in other latitudes. An apparent corollary 

 of this conclusion is that these changes were due to a shifting of the world's climatic zones 

 because of an alternate increase and decrease in the intensity of atmospheric movements, 

 but this corollary has by no means the same degree of probabiUty as the main conclusion 

 whose verity it in no wise affects. 



The third of our conclusions depends upon the verity of the first two. The agreement 

 of the mathematically derived curve of the sequoias with the Asiatic curve based on totally 

 different kinds of evidence seems to confirm the vaUdity of the methods employed in dealing 

 with those other kinds of evidence. This confirmation has important consequences. 

 In all studies of the climate of the past it is far easier to see and interpret signs of the 

 general prevalence of relatively moist conditions than to see and interpret the signs of 

 climatic pulsations. On this rock, almost without exception, careful students of the 

 subject have come to grief, for as soon as they have perceived evidences of a degree of 

 aridity in remote historic times at all approaching that of to-day, they have jumped to the 

 conclusion that such conditions have prevailed always, instead of only temporarily. If 

 the methods which were first employed in Asia and Greece, and have now been applied 

 to America, as set forth in the first part of this volume, are competent to accomplish the 

 task of correctly dating the chief climatic pulsations, it seems as if they must be competent 

 to accomplish the easier task of determining whether the climate of the past as a whole 

 was different from that of the present. They point to this conclusion more strongly than 

 to that of pulsatory changes. Hence we conclude not only that the climate of both America 

 and Asia has been subject to pulsations, but that in general the average conditions of 2,000 

 or 3,000 years ago were moister than those of to-day. This is the reason for adjusting the 

 general level of the earlier part of the sequoia curve by means of the variations in the level 

 of the Caspian Sea, and for believing that the curve thus adjusted represents the approxi- 

 mate truth as to the climatic pulsations of temperate continental regions for the past 3,000 

 years. 



