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their fluctuations. It is found that the changes, though moderate in amount, 

 are more or less sudden and pulsatory. In the search for causes Huntington 

 consequently assigns crustal movements and changes in atmospheric composi- 

 tion as the broad factors of ultimate control, but the pulsations which appear 

 within the historic record and which extend beyond in the record of moraines 

 left by the oscillations of glaciers, the strands of salt lakes, and terraces 

 made by river action cannot, he argues, be due to these causes. Variations in 

 solar radiation are assigned as the most probable cause. Rhythms measured 

 by tens of miles marked the retreat of the Pleistocene ice sheets; rhythms 

 measured by inches, by feet, and by tens of feet are found in the sediments 

 of many geological formations. In many cases they can hardly be ascribed 

 to crustal causes; they are too many and both too long and too short to fit the 

 precession cycle. Thus the geological record is suggestive that our sun through 

 all of terrestrial history has been a variable star. 



The second part of the volume consists of a chapter entitled "The Climates 

 of Geologic Time, and is by Professor Schuchert. There is assembled in 

 thirty pages an account of the various lines of evidence which indicate geologic 

 changes in climate. These are finally correlated in a single chart. The curves 

 of coal-making, limestone-making, aridity, and temperature are given, together 

 with curves showing the movements of the strand line and epochs of diastro- 

 phism. While the curves are of course only of qualitative value, they serve to 

 show the variability and the cyclic nature of all these factors through geologic 

 time. This chapter thus gives on a large scale and in distant perspective what 

 the first part of the book gives in minute scale and for the human present. 



It would appear that the work of Douglass and Huntington on tree growth 

 opens up a field which deserves further study; a study which should be prose- 

 cuted within a few years. In this reconnaissance Huntington has averaged 

 together the measurements of many individual trees. But these have grown 

 under unlike conditions of altitude, slope exposure, and ground water. The 

 averaging of these unlike conditions has tended toward obscuring the amount 

 of short climatic oscillations and the trend of longer changes. An intensive 

 study of stumps selected with respect to these variable controls and an exact 

 dating of special sequences of rings by comparison of stumps would seem to 

 be the next step. But in the meantime decay is blurring year by year this 

 most valuable record. 



There are of course in this volume degrees of emphasis and points of 

 view which could be questioned, but within the limits of a short review it 

 would confer a wrong emphasis to single out any point for critical comment, 

 when the book as a whole is a contribution of the first order, in facts, in ideas, 

 and in completeness of presentation. It adds fundamentally to the science 

 which in the future will be named if not now — paleoclimatology. 



J. B. 



