THE 



GEOLOaiCAL MAGA^ZINE. 



NEW SERIES. DECADE II. VOL. III. 



No. IX.— SEPTEMBER, 1876. 



OIRXG-XISTJ^Xj J^iK^TIOXiIES. 



I. — The Climate Controversy. 

 By Searles V. Wood, Jun., F.G.S. 



THE cause of changes in Climate during past Geological periods 

 having lately become, and being likely to continue, a prominent 

 topic of interest, I have attempted here to bring together the more 

 prominent features in the controversy, under the idea that to many 

 readers, who have not either the time or the inclination to more 

 closely examine the subject, this may be acceptable. In so doing I 

 have, with one partial exception, confined myself to discussing the 

 difficulties which beset all the various theories offered as a solution, 

 rather than attempted the advocacy of any one of those theories in 

 particular. 



The following seven causes have been advanced, at various times, 

 to account for the changes in Climate, which the evidence of the 

 Geological record proves have taken place during that portion of 

 the Earth's history which it covers. 



1. A decrease in the original heat of our planet. 



2. Changes in the obliquity of the ecliptic. 



3. The combined effect of the precession of the equinoxes, and of 

 the excentricity of the Earth's orbit. 



4. Changes in the distribution of land and water. 



5. Changes in the position of the Earth's axis of rotation. 



6. A variation in the amount of heat radiated by the Sun. 



7. A variation in the temperature of those regions of space through 

 which the solar S3'stem has moved. 



No. 1. — Since all physicists are agreed that the earth has under- 

 gone a process of cooling, the main questions that have arisen under 

 this head are: what has been the effect of this cooling upon the 

 temperature of the earth's surface, and whether evidences of such 

 refrigeration can be traced in the Geological record ? 



As to the first of these questions, a celebrated physicist is of 

 opinion that the influence of the earth's proper heat on climate is 

 not only inappreciable at the present day, but must always have 

 been so since the condition of the crust allowed of the existence of 

 life upon the earth. As to the second, it must be admitted that 

 organic remains throw but little light upon it. Beyond the fact that 

 at the present day reptile-life cannot exist in very cold climates, and 

 seems to prevail in the direct ratio of the warmth of the air or water 

 in which it lives, there is but little to show that the climates of those 



DECADE II. — VOL. III. NO. IX. 25 



