INTRODUCTION. 5 



It is true that attempts to detect such results have hitherto proved contradictory, but 

 this is not surprising. It seems to be due partly to the lack of long, homogeneous records 

 and partly to failure to make due allowance for the different degrees to which different kinds 

 of phenomena, such as temperature, pressure, wind, and rain, must lag behind their cause, 

 especially under conditions such as those of the atmosphere, where large quantities of heat 

 are transferred from one region to another. The new method of investigation of cKmate 

 by means of the growth of trees, as elaborated by Professor Douglass in his contribution 

 to this volume, furnishes long, homogeneous records, and these show a distinct sun-spot 

 cycle. The careful researches of Arctowski upon "pleions" and "anti-pleions" seem not 

 only to demonstrate a relation between solar phenomena and terrestrial chmate, but also 

 to show why the manifestation of this relationship is irregular and, at first sight, con- 

 tradictory. These tilings lead to the conclusion that the small climatic cycles now in 

 progress upon the earth are in large measure due to variations in the sun. 



In regard to greater climatic changes, it appears that the pulsations of the past 3,000 

 years are too large to be due to fortuitous rearrangements of the earth's atmosphere because 

 of purely terrestrial causes. On the other hand, they occur too rapidly to be due to pre- 

 cession of the equinoxes, changes in the carbonic-acid content of the air, or deformation 

 of the earth's crust. Hence we are led to conclude that they, too, are due to variations 

 in the sun. The same conclusion seems to apply to glacial and interglacial epochs, since 

 their characteristics ajipear to be identical in nature with those of the pulsations of historic 

 times, although differing greatly in degree. In explanation of still greater changes, how- 

 ever, such as the radical difference between the distribution of climatic zones in the Permian 

 and Pleistocene eras, something else is demanded. In Part II of this volume the matter 

 is fully presented by Professor Schuchert from the standpoint of the paleontological geolo- 

 gist. We are there led to the conclusion that while changes in the amount of carbonic-acid 

 gas in the atmosphere may explain certain climatic phenomena, they can not explain this 

 particular feature. Crustal deformation, on the contrary, seems fully adequate to cause 

 just such a redistribution of zones as we find from time to time in geologic history. It 

 apparently can not, however, account for the climatic instability which often accompanies 

 or immediately follows periods of crustal deformation, that is, for fluctuations from glacial 

 to interglacial conditions and for minor pulsations. In explanation of these it seems 

 reasonable to turn back to our solar hypothesis. Thus we are led to the final hypothesis 

 that for some unknown cause both the earth and the sun have been repeatedly thrown into 

 activity at approximately the same time. The activity of the earth seems to manifest itself 

 in the changes of form whereby continents are uplifted and mountain ranges shoved up. 

 That of the sun seemingly displays itself in pulsations which give rise to climatic variations 

 of every grade, beginning with glacial and interglacial epochs and ending with little cycles 

 like that of the sun-spots. 



Here we leave the matter, but not without a word of caution. Throughout this volume 

 our purpose is not to develop the hypothesis just outlined as to the interrelation of solar 

 activity, crustal deformation, and climatic changes. That hypothesis, important as it 

 may prove, is by its very nature open to grave question. At best it is merely a corol- 

 lary of our main conclusion, whose truth or falsity is in no way dependent upon it. The 

 primary purpose of this book is to investigate any possible climatic changes which may 

 have taken place in historic times. Our main conclusion is that such changes have taken 

 place and that they have been of a pulsatory nature. All other questions are here sub- 

 ordinate, and the truth or falsity of this conclusion is the point upon which attention 

 should be focused. 



