we may know exactly how, when, and why the limits of cultivation expanded and contracted. In general, however, it appears that the history of the rise and fall of successive phases of civilization in Mery 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 a climatic theory in 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.
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