566 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



evidence which points to alternate Glacial and inter-Glacial epochs. It 

 seems safe to say that the vast majority of geologists agree that Glacial 

 epochs have succeeded one another too rapidly to allow us to entertain 

 the hypothesis that they are due primarily to crustal movements. Such 

 movements probably prepared the way for the Glacial period by raising 

 the continents to a great altitude, but their work ended at that point. 



These considerations, together with what has already been said as to 

 the meteorological and volcanic hypotheses, seem to limit our choice to 

 the carbonic acid hypothesis and the solar hypothesis in one or the other 

 of its forms. The carbonic acid hypothesis ranks as one of the great 

 contributions to geology. Whether right or wrong, it has been remark- 

 able for the extent to which it has stimulated investigation. The study 

 of that hypothesis and a whole-hearted acceptance of it furnished one of 

 the strongest of the stimuli which led to the present paper. The care 

 with which it has been worked out and the admirable manner in which 

 it has been presented will long serve as a model for geological work. I 

 can not too strongly express my feeling of indebtedness to that hypothesis 

 and of admiration for the way in which it has been framed. 



THE CARBONIC ACID HYPOTHESIS 



The cyclonic solar hypothesis and the carbonic acid hypothesis are not 

 necessarily antagonistic. Both may contain large elements of truth, for 

 one may explain climatic variations of very long duration, while the other 

 may explain those of shorter period and quicker activity. Turning di- 

 rectly to the carbonic acid hypothesis, the first thing to be pointed out is 

 that its supporters do not invoke it as an explanation of such brief 

 changes as those which appear to have occurred during the past two or 

 three thousand years. Even when it comes to Glacial stages they hesitate 

 somewhat in its application. Others who are not so "directly interested 

 in it believe that it can not act quickly enough even to produce Glacial 

 epochs. Its fundamental requirement is that changes shall be slow. A 

 change in a given direction can be reversed only by a highly complicated 

 rearrangement of the composition and movements of both the air and the 

 ocean. Hundreds of thousands instead of mere hundreds of years are 

 required to produce noteworthy effects. It is highly probable that 

 changes in the carbonic acid content of the air are an important climatic 

 factor. It scarcely seems possible that enormous amounts of COg should 

 at some periods be locked up in coal and limestone and at other periods 

 be set free without altering the composition of the earth's atmosphere. 

 Such alterations can scarcely fail to produce an effect on climate, espe- 

 cially through their alteration of the power of the atmosphere to hold 



