REVIEWS 95 



author. Especially interesting are the life-restorations, some of which 

 are here published for the first time. There is no one better fitted to 

 discuss the subject-matter contained in this book than the author of 

 this volume. In it he gives to the public the benefit of his observations 

 gathered from over forty years of actual experience in the reptilian 

 field. It is rare indeed that a subject is given such an authoritative, 

 scientifically exact treatment combined with a style so thoroughly 

 understandable and interesting to the non-scientific reader. The work 

 is sure to be very popular with the scientist and the general public alike. 



M. G. Mehl 



The Climatic Factor as Illustrated in Arid America. By Ellsworth 

 Huntington, Assistant Professor of Geography in Yale 

 University, with contributions by Charles Schuchert, 

 Andrew E. Douglass, and Charles J. Kullmer. Carnegie 

 Institution of Washington, Publication No. 192, 1914. Pp. vi 

 +341, plates 12, maps 2, text figs. 90. 

 This volume has bearings which make it important to the geographer, his- 

 torian, archeologist, meteorologist, and geologist, occupying a field where all 

 these sciences meet, but in this review the volume will be discussed from the 

 geological point of view only. 



The purpose of the work is to determine the degree to which climatic 

 changes have taken place in southwestern America during the past 2,000 to 

 3,000 years. In arid and semi-arid regions the amount of rainfall, as affected 

 by pulsatory changes of climate, becomes most variable and critical. 



In addition to the study of the climatic changes shown by the expansion 

 and restriction of ancient peoples in America, as controlled by changes in 

 water-supply or vegetation, the present volume contains two novel lines of 

 attack. The first of these is the use of river terraces as evidences of minor 

 climatic changes occurring within the past few centuries as well as in the more 

 distant past. The second is the measurement of the growth rings of trees. 

 Professor A. E. Douglass gives an introductory chapter on a method of esti- 

 mating rainfall by the growth of trees. He shows that the rings vary in thick- 

 ness and correlates the rate of growth with the records of rainfall. Following 

 this, Huntington enters upon a most interesting discussion of the curve of 

 growth of the giant redwoods of California. The data were obtained by 

 careful measurements from stumps and extend back with a large number of 

 trees as much as 2,000 years, with a few trees to 3,000 years. The geological 

 importance of this work is readily seen. As LyeU showed that the present 

 is the key to the past in the crustal history of the earth, similarly the key to 

 the climatic history is to be found in the study of the present climates and 



