APPENDIX. 



291 



times traversed more or less heated zones of space, giving 

 alternations of warm and cold temperature. No such 

 differences in space are, however, known, nor does there 

 seem any good ground for imagining their existence. 



7. The differences in the form and elevation of our continents, 



and in the consequent distribution of surfaces of different 

 absorbent and radiating power, and of the oceanic 

 currents, are known causes of climatal change, and 

 have been referred to in these papers as competent to 

 account for many, at least, of the phenomena. 



8. Reference has already been made, in connection with the 



distribution of plants, to the possibility that the primeval 

 atmosphere was richer in carbon than that of more 

 modern times, and that this might operate to produce 

 diminution of radiation, and consequent uniformity of 

 temperature ; but this cause could not have been efficient 

 in the later geological periods. 



Sir William Dawson having further reviewed the fourth 

 and seventh theories enumerated by Mr. Wood, urges the 

 sufficiency of the old Lyellian theory of geographical 

 changes, with such modifications as recent discoveries have 

 rendered necessary to account for facts. — Ed. 



