1 88 EVOLUTION OF THE EARTH 



southward tendency. Its center sweeps across the Great Lakes, 

 and then swings northeastward down the St. Lawrence River 

 to the Atlantic south of Newfoundland. It crosses the Atlantic 

 to Europe, where it splits up, and almost dies out in Siberia and 

 central Asia. On the eastern border of Asia it is joined by 

 an important and vigorous branch from Japan, and then skirts 

 the Pacific coast of North America to British Columbia. Its 

 course may be judged from Figure 34, where in general the 

 dark areas of high energy are also stormy areas. The other, 

 or minor storm belt, appears to start in California, cross 

 Arizona and New Mexico to the Gulf of Mexico, and then 

 swing northeastward into the Atlantic Ocean. In the Old 

 World its course lies along the Mediterranean, beginning ap- 

 parently east of Spain. Beyond the Mediterranean it passes 

 across Syria to Mesopotamia and Persia, and then in an attenu- 

 ated form to India. It probably revives again in China and 

 joins the strongly developed Japanese area of storms. In the 

 past, at times when rainfall has been abundant in Mediterra- 

 nean lands, many storms appear to have followed this southern 

 belt. Thus increased rainfall and increased variability oc- 

 curred during certain centuries, while the opposite occurred 

 in others. The centuries which saw increased rainfall in the 

 subtropical belt saw decreased rainfall farther south in places 

 like Yucatan, on the northern border of the torrid zone, but 

 with this decreased rainfall also went greater variability be- 

 cause of the storms whose centers passed a little farther north. 

 Hence it appears that not only in our own day, but throughout 

 historic times the highest civilization has been found in the 

 regions of greatest climatic energy. 



The possible exceptions to this conclusion are the areas of 

 high civilization within twenty-five degrees of the equator. 

 These include Central America, the highlands of Peru, Yemen 

 and Rhodesia, Indo-China, and some of the East Indies like 

 Sumatra and Java. None of these places, however, made any 



