232 KURGANS OF THE MERV OASIS. 
we may know exactly how, when, and why the limits of cultivation expanded and con- 
tracted. In general, however, it appears that the history of the rise and fall of successive 
phases of civilization in Merv corresponds to what would be expected in view of the theory 
of climatic changes outlined above. A fuller study of the region will afford one of the best 
possible tests of the theory. The matter is referred to here thus briefly in order to explain 
why it is that the writer, having advanced aclimatic theoryin explanation of certain great 
historic events, such as the barbarian invasion of Europe in the Dark Ages, here publishes 
a chapter upon one of the most critical regions to be found anywhere in the world, and 
devotes only a page or two to the most elementary phases of the question. The chapter 
is one of the steps which led to the theory, and therefore takes up only the rudiments 
of the subject. 
