280 



APPENDIX. 



CAUSES OF CLIMATAL CHANGES. 



The discussion upon Professor Geikie's valued paper hav- 

 ing tended to show how diverse are the views held upon this 

 subject, it may be permitted to quote certain remarks made 

 "On the Causes of Climatal Changes," by Sir J. William 

 Dawson, C.M.G., F.R.S., in his last new work.* 



The subject ... is one which has been in dispute ever since 

 I began to read anything on geology, nearly sixty years ago. It 

 ought to have been settled, but up to to-day one finds in geological 

 works and papers — especially those relating to the Glacial age — 

 the most divergent views. 



Mr. Searles V. Wood, in an able summary of the possible 

 causes of the succession of cold and warm climates in the northern 

 hemisphere, enumerates no fewer than seven theories which have 

 met with more or less acceptance, and he might have added an 

 eighth. These are : — ■ 



1. The gradual cooling of the earth from a condition of original 



incandescence. 



2. Changes in the obliquity of the ecliptic. 



3. Changes in the position of the earth's axis of rotation. 



4. The effect of the precession of the equinoxes, along with 



changes of the eccentricity of the earth's orbit, 

 o. Variations in the amount of heat given off by the sun. 



6. Differences in the temperature of portions of space passed 



through by the earth. 



7. Differences in the distribution of land and water in connec- 



tion with the flow of oceanic currents. 



8. Variations in the properties of the atmosphere with refer- 



ence to its capacity for allowing the radiation of heat. 



* Some Salient Points in the Science of the Earth. Hodder and Stough- 

 ton. 18D3. This valuable work is " intended as a closing deliverance on 

 some of the most important questions of Geology, on the part of a veteran 

 worker." 



