Prehistoric Droughts in the Central Great Plains

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T HE recent succession of dry years in the Great Plains and particularly the devastating droughts of I934 and I936 have once again focused attention on the fluctuations of precipitation to which our subhumid and semiarid lands in the West are subject. During the first two decades of the twentieth century precipitation in the Great Plains was generally above normal, and this fact in conjunction with the great profits made in wheat farming during the World War tended to obliterate all memory of the drought years of the nineties and other periods of serious moisture deficiency within historical times. There is little doubt in the minds of students of weather and climate that wide borderland areas between humid and arid regions will always be subject to recurrent droughts of varying duration and intensity, such as those experienced in historical times. Also, before the dawn of recorded history droughts occurred, some of which were brief, others evidently very long. An increasing volume of evidence points to the occurrence, after the close of the Pleistocene epoch, of several climatic fluctuations of long range and fairly wide amplitude that probably affected most of eastern North America. According to the data available at present, it seems that these long periods, during which average temperature and average precipitation were different from the averages of today, were similar to the periods that have been fairly well established for Europe.1 Of these periods, the two driest ones (the Boreal, from 8ooo to 5000 B.C.?, and the Sub-Boreal, from 2000 to 600 B.C.?) were probably much drier in the Great Plains than anywhere farther east, assuming, of course, that present regional differences of climate already existed, though possibly in somewhat modified form. Botanical evidence, both that offered by the present distribution of plants and that offered by the stratigraphy of peat bogs, seems to favor such longrange climatic changes. Physiographic evidence also, if carefully evaluated and interpreted, may prove to be an important aid in studying this problem. Ellsworth Huntington and others2 have drawn attention to the climatic origin of certain river terraces. Morphologically young terraces bearing all the earmarks of a climatic