60 BUREAU OF AMERICAN ETHNOLOGY* [bull. 54 



course, be due to disease, insects, or other causes. Not having 

 examined the region referred to by Newberry, the writers have no 

 information except what is contained in the foregoing quotation, but 

 this e\'idence may not demonstrate increasing dryness. Perhaps none 

 of the other hues of evidence alone woukl prove the point, but so 

 many converging hues, all suggesting the same explanation, increase 

 the probability that tliis is the true explanation. 



Geological Evidence of Change of Climate 



In geologic literature changes of climate during the past ages have 

 been much discussed, especially, though by no means altogether, in 

 connection with glacial epochs. In the early stages of geologic 

 science it was supposed that there had been a rather uniform cooling 

 of the earth from a molten condition to its present state, with a conse- 

 quent uniform progressive change of climate from a supposed original 

 warm moist climate to that of the present, with its extremes of tem- 

 peratm'e and moisture. That supposition was the natural outgrowth 

 of the nebular hypothesis in its earlier form. Gradually accumulat- 

 ing evidence compelled the abandonment of that idea, as it became 

 known that glaciation, desiccation, and other changes of climate had 

 alternated throughout the past ages, instead of there having been 

 progressive change in one direction. The so-called Glacial epoch, for 

 example, was but one of several such epochs extending from Cam- 

 brian or pre-Cambrian to Pleistocene time, so that recently it has 

 been well said that "there is no evidence known to the geologist of 

 any progressive refrigeration of the earth." ^ To satisfy the demands 

 of this and of other important facts, the planetesimal hypothesis has 

 been proposed as a modification of or a substitute for the nebular 

 hypothesis.^ While geologic discoveries indicate that there has been 

 no general progressive change in one direction, it seems settled that 

 there have been repeated fluctuations throughout the past. Perhaps 

 the most radical change of climate was during Pleistocene time, 

 the period which immediately preceded the present, and, indeed, may 

 be considered to extend into and cover the present time. During 

 this period occurred the great Glacial epoch, in which a thick sheet of 



' Gregory, J. W., Climatic Variations: Their Extent and Causes, in Smithson. Rep. for 1908, p. 339, 

 1909 (address before the Mexico City session of the International Geologic Congress). See also on various 

 climatic changes in the past, among others, the following: Chamberlin, Thomas C, and Salisbury, RoUin 

 D., Geology, l, 643; II, 273, 343, 387, 396, 518, 669; UI, 29, 79, 129, 161, 172, 261, 281, 316, 325-515; 1905 and 1906; 

 White, David, and Knowlton, F. H., Evidences of Paleobotany as to Geological Climates, in Science, 

 n. s., XXXI, 760, 1910; Reid, H. F., Mr. Manson's Theory of Geological Climates, ibid., xxix, 27-29, 

 1909; Coleman, A. P., Glacial Periods and Their Bearing on Geological Theories, ibid., xxvn, 406, 1908; 

 A Lower Huronian Ice Age, ibid., xxv, 769, 1907; Arnold, Ralph, Environment of the Tertiary Faunas 

 of the Pacific Coast of the United States, in Journ. Geol, xvn, 509-33, 1909; White, David, Permo- 

 Carboniferous Climatic Changes in Brazilian South America, as Indicated by Fossil Plants, in Science, 

 n. s., xxv, 772, 1907. 



2 Chamberlin, Thomas C, and Salisbury, Rollin D., Geology, ii, 38-81, 1906; Chamberlm, Thomas C, 

 A Geologic Forecast of the Future Opportunities of Our Race, in Science, n. s., xxx, 938-49, 1909. 



