Climatology 131 



CLIMATOLOGY, ETC. 



No. 192, HUNTINGTON, ELLSWORTH, with contributions by CHARLES SCHUCHERT, 

 A. E. DOUGLASS, and CHARLES J. KULLMER. The Climatic Factor, as 

 illustrated in Arid America. Quarto, 341 pages, 12 plates, 2 maps, 90 

 figures. Published 1914. Price $5.50. 



This study of changes of climate is a continuation of the work described in the 

 author's papers in Nos. 26 and 73. It deals mainly with the relation of climate to 

 geological, botanical, and archeological phenomena, but contains also a considerable 

 amount of geographical description. The book begins with a discussion of the 

 present climate of Arizona and New Mexico, and its effect upon the earth's 

 surface and upon vegetation. Because of the aridity and scanty vegetation, 

 deposits of alluvium are abundant and many are terraced. A consideration of 

 whether these terraces are of climatic or tectonic origin leads to the conclusion that 

 they are climatic, and that they indicate climatic pulsations during the period of 

 human occupation. Numerous ruins, here and in Mexico, Yucatan, and Guatemala, 

 point to the same conclusion and suggest the existence of at least three moist 

 periods separated by times of aridity. 



An independent investigation of the same problem, based on the method of 

 Prof. A. E. Douglass, shows that the amount of rainfall may be determined from 

 the thickness of rings of growth in trees. From measurements of 450 Sequoias in 

 California a curve has been plotted showing the approximate pulsations of rainfall 

 in California for 3,000 years. Comparison with meteorological records suggests 

 that the pulsations consist of an alternate weakening and strengthening of atmos- 

 pheric circulation, whereby climatic zones are moved first poleward, then equatorward. 



This conclusion leads to an attempt to determine the cause of changes of cli- 

 mate, including not only recent changes, but those of geological times, which 

 are discussed by Professor Schuchert, who lays special emphasis upon the im- 

 portance of broad crustal deformation. Such deformation, however, can scarcely 

 account for glacial and inter-glacial epochs, and much less for the pulsations in- 

 dicated by the California trees. Only the solar hypothesis seems adequate. This 

 conclusion is tested by investigating the possibility of a connection between varia- 

 tions in sun spots and changes in the growth of trees. Such a connection seems 

 to exist, and various phenomena suggest that apparent discrepancies are in reality 

 results that would naturally be expected. 



Chapters 2, 4, 5, 6, and 10 deal with the geological problem of the effect of 

 aridity upon surface forms and upon subaerial deposits. The problem of the tec- 

 tonic versus climatic origin of alluvial terraces in dry mountain regions is treated 

 at length. Chapters 19, 20, and 21 discuss theories of climatic changes, special em- 

 phasis being given to the solar hypothesis as the cause of changes of the magni- 

 tude of glacial epochs or less, and to crustal deformation as the cause of greater 

 changes, such as glacial periods. 



Inasmuch as botanical evidence is largely used in elucidating the climate of the 

 past, Chapter 2 describes the arboreal desert of the southwestern United States. 

 Chapters 11 to 14 discuss the relation of the thickness of rings of growth to 

 climatic conditions, not merely in the case of the Sequoia of California, but among 

 trees from all parts of the country. The evidence presented in Chapters 15, 16, 

 and 17 suggests that in equatorial regions plant formations may be displaced by 

 climatic changes with a degree of rapidity which must cause the process of natural 

 selection to act with greater speed than is commonly supposed. 



The climate of the past stands in vital relation not only to geology and botany, 

 but to men. Hence it is necessary to consider fully the ruins of the Southwest and 

 the conditions under which the people lived. This is done in Chapters 6 to 10. 

 The ruins and civilization of the Mayas in Yucatan and Guatemala are also im- 

 portant lines of evidence, and in Chapters 15 to 18 the theory is advanced that 

 when the Mayas were in their prime the lowlands of this region were decidedly 

 drier than now. 



