THE EXAMPLE OF ROME 187 



evidence of climatic changes. In the publications listed in the 

 Appendix, I have gone into the matter in great detail. Here it 

 is enough to say that after a decade of vigorous discussion the 

 geographers of America, and to a considerable degree those of 

 other countries also, seem to have come to the conclusion that 

 climatic pulsations of considerable amplitude have occurred 

 during historic times. As Colton puts it : "The summation of all 

 these different lines (of evidence) makes the theory of climatic 

 pulsations become the doctrine of climatic pulsations." More- 

 over, Antevs has carried out a most careful study of all that has 

 ever been written on "The Annual Rings of Tree Growth and 

 Their Meaning as Climatic Indicators." He believes that the 

 present author has underestimated the magnitude of the climatic 

 pulsations indicated by the trees of California. 



The best available measure of the climate of the past is the 

 growth of the Big Trees of California as determined by the width 

 of the annual rings of hundreds of stumps. The curve thus 

 obtained is shown in Figure 24. Where it is high the climate was 

 relatively moist and rainy, and storms were abundant so that the 

 stimulating qualities were at a maximum. Where it is low the 

 reverse conditions prevailed. Since the southern half of Cali- 

 fornia and the southern half of Italy lie in essentially the same 

 kind of climate, the pulsations of the two places appear to be 

 practically the same. That this is so appears from the rainfall 

 of March to July, the critical months for agriculture and tree 

 growth. Let us compare the rainfall at San Diego and San Fran- 

 cisco since 1851 with the growth of one hundred and twelve sequoia 

 trees in the Sierra Nevada Mountains and with the rainfall in 

 Italy. We will arrange the years of each record in order accord- 

 ing to the amount of rain in California, and then divide them into 

 the four groups indicated below. For the trees, however, we will 

 use first the three-year period beginning with a certain condition 

 of rainfall (E), and second the growth in the third year of each 

 three-year period (F). This is because the huge sequoia trees 



