486 HUNTINGTON— GUATEMALA AND THE [April i8. 



ruins of Maya culture lie upon a terrace of exactly this sort, while 

 below the ruins there lies another similar terrace formed since the 

 ruins were built. This seems to indicate that since the foundation of 

 Copan, probably early in the Christian era, there has been a double 

 climatic change whereby the Copan River, after having filled up 

 its valley to the level of the upper terrace, was then impelled, first, to 

 carry away material from the valley bottom, next to deposit new 

 material, and again to carry it away. In other words the terraces 

 seem to afiford independent evidence that since the building of 

 Copan the climate of Guatemala has been subject to distinct pul- 

 sations. 



The other line of evidence is so complex that only the results can 

 here be stated. From a prolonged study of ruins in dry places, 

 roads and deserts which are now impassable, traces of springs where 

 no springs now exist, elevated strands of enclosed salt lakes, and 

 other lines of historic, archaeological and physiographic evidences 

 the writer has been led to believe that in central and western Asia, 

 Greece, north Africa and perhaps elsewhere climatic pulsations 

 have taken place during historic times. A study of similar lines of 

 evidence in the United States under the auspices of the Carnegie 

 Institution in the years 1910-1912 led to a similar conclusion here. 

 Finally still another independent line of research was adopted, 

 namely the measurement of the rate of growth of the giant sequoia 

 trees of California which grow in a region where the thickness of 

 the rings depends largely upon the amount of rainfall. This led 

 to the same conclusion, namely that pulsatory changes of climate 

 have taken place to a marked degree during the past three thousand 

 years. The nature of the change has been inferred from various 

 sources, especially from a comparative study of the meteorological 

 records during years when the trees of California grew rapidly or 

 slowly during the last half century. From this it appears that moist 

 periods in regions like Persia, Greece or Arizona are probably due 

 to the fact that the cyclonic storms of winter not only move far- 

 ther south than usual and hence are uncommonly frequent in those 

 countries but perhaps begin earlier in the fall and last longer in the 

 spring. This, of course, reduces the length of the dry season in 

 summer. 



