MODIFICATION OF THEORY EXAMINED. 95 



geographical distribution of land and water permitting 

 of the existence and deflection of those heat-bearing 

 currents is one of the main factors in my theory is what 

 must be obvious to every reader of ' Climate and Time.' 



The difference between Mr. Wallace and myself is 

 this : — I maintain that with the present distribution of 

 land and water, without calling in the aid of any other 

 geographical conditions than now obtain, those 

 physical agencies detailed in ' Climate and Time ' are 

 perfectly sufficient to account for all the phenomena 

 of the glacial epoch, including those intercalated warm 

 periods, during which Greenland would probably be 

 free from ice and the Arctic regions enjoying a mild 

 climate ; while Mr. Wallace, on the other hand, 

 maintains that without assuming some change in the 

 geographical conditions of our globe those physical 

 agencies will not account for that state of things, at 

 least in so far as the disappearance of the ice in Arctic 

 regions is concerned. 



To narrow the field of inquiry, and bring more 

 prominently before the mind the real question at issue, 

 I shall state the main points on which Mr. Wallace 

 and I appear to agree. 



Points of agreement. — 1. Mr. Wallace agrees- with 

 me that a high state of eccentricity could never 

 directly produce a glacial condition of climate ; that 

 the glacial epoch was the direct result, not of a high 

 state of eccentricity, but of a combination of physical 

 agencies brought into operation by means of this high 

 state. 



2. He agrees with me also in regard to what these 

 physical agencies really were ; for the agencies to 

 which he refers in his " Island Life " are almost 

 identically those which I have advanced in ' Climate 

 and Time ' and elsewhere. 



