8 
THE SECRET OF THE BIG TREES. 
has not proceeded regularly, however, but in a pulsatory fashion. It 
seems to have been interrupted by centuries of exceptional aridity 
on the one hand and of exceptional moisture on the other. When 
these pulsations of climate are compared with the course of history 
a remarkable agreement is noticed. Among a mass of minor details 
this apparent relationship may be concealed, but the broad move¬ 
ments of races, the rise and fall of civilization, seem to show a de¬ 
gree of agreement with climatic changes so great that it scarcely 
seems possible to avoid the conclusion that the two are intimately 
related. Unfavorable conditions of climate, such as a change toward 
aridity in regions already none too well supplied with water, have 
apparently led to famines, epidemics, economic distress, the decline 
of trade, misgovernment, migrations, wars, and stagnation; while 
favorable changes have fostered exactly opposite conditions. 
This theory strikes so profoundly at the roots of all historical in¬ 
terpretation and is of such fundamental importance in its bearing 
on the future of nations and of the human race as a whole that it 
demands most careful testing. The first step in carrying on the 
necessary tests is obviously to determine the exact degree of accuracy 
of our conclusions as to the dates and nature of climatic changes. 
Only when that has been done are we prepared to proceed to a fuller 
investigation of the relation of the changes to historic events. 
After some years had been spent in a study of this great problem 
from various standpoints in Asia, the logical thing seemed to be to 
take up the same lines of work in some other continent and see how 
far the two agreed. Fortunately I was invited by Dr. D. T. Mac- 
Dougal to cooperate with the Department of Botanical Research of 
the Carnegie Institution of Washington in a study of the climate of 
the southwestern part of the United States. In general the phe¬ 
nomena of ancient ruins, old strands of inclosed salt lakes, the gravel 
terraces of rivers, and the distribution and agriculture of the prehis¬ 
toric population seemed to indicate that the climatic history of Amer¬ 
ica has been the same as that of Asia. The results, however, were 
unsatisfactory in two respects. In the first place, previous to the 
time of Columbus we know almost nothing about the dates of events 
in America, and hence it is impossible to know whether the apparent 
climatic fluctuations of America agree in time with those of Asia. 
In the second place, a theory is a dangerous thing. Strive as he will, 
the author is apt to be partial to it and to interpret all that he sees in 
such a way as to fit his preconceived ideas. During my work in Ari¬ 
zona, !New Mexico, and old Mexico I knew that when its results were 
announced critics would say, “ That is all very interesting, but not 
convincing. You went out West expecting to find evidences of 
pulsatory changes of climate during historic times, and, of course, 
you found them. We will wait a while before we believe you.” 
