1913-] HIGHEST NATIVE AMERICAN CIVILIZATION. 485 



is to-day difificult would be reduced. Debilitating malarial fevers 

 would prevail but little under such conditions, and the fact that 

 Peten is a lowland, fertile and easily accessible, would make it a 

 natural center of civilization. In other words if we adopt a climatic 

 hypothesis of the kind here outlined, it does not lead us to abandon 

 our other hypotheses as to the racial character of the Mayas, or as 

 to the debilitating effects of disease. It simply supplies the ele- 

 ments which the other hypotheses lack. 



The hypothesis of a change of •climate in Guatemala by no means 

 finds its only support in the considerations just set forth. On the 

 contrary two independent lines of reasoning lead to the same con- 

 clusion. One of these is the existence of alluvial terraces in close 

 connection with the ruins of Copan, and the other is the logical 

 result of the investigation of ruins, lakes, and deserts in Asia, and 

 of similar phenomena together with the growth of trees in North 

 America. Both must be dismissed brieiiy. During the Pumpelly 

 expedition sent out by the Carnegie Institution of Washington to 

 Central Asia in 1903, Professor William M. Davis and the writer 

 investigated a large number of alluvial terraces in mountain valleys 

 from Persia eastward to Chinese Turkestan. From various lines 

 of evidence set forth in the report" of that expedition they came to 

 the conclusion that the terraces must be due to variations of climate. 

 Otherwise they could scarcely occur with such a wide and regular 

 distribution, and with such a minute adaptation to every valley no 

 matter which way it sloped or how large it might be. Further study 

 in the drier parts of the United States and northern Mexico as well 

 as in Greece and Turkey seems to confirm this idea. It has been 

 found, furthermore, that terraces of the same kind and apparently 

 of the same climatic origin extend down into Southern Mexico and 

 are well developed in the state of Oaxaca. In Guatemala the 

 Motagua and other rivers are characterized by similar terraces which 

 are described in full in the author's forthcoming volume on the 

 " Climatic Factor " to be published shortly by the Carnegie Institu- 

 tion of Washington. It must suffice to say here that the famous 



- " Explorations in Turkestan," Vol. i, 1905, Carnegie Institution of 

 Washington, Publication No. 26. 



