90 Dr. J. Oroll on the Physical Theory 



which deflected the equatorial current into the Southern Ocean. 

 That a 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 w T hat 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 pro- 

 bably 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 con- 

 ditions of our globe those physical agencies will not account 

 for that state of things, at least in so tar 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 t Island Life ' are almost identically those which I have 

 advanced in c Climate and Time ' and elsewhere. 



3. Mr. Wallace agrees with me in regard to the mutual 

 reactions of the physical agents. He maintains with me that 

 these physical agencies not only all lead to one result — the 

 accumulation of snow and ice — but that their efficiency in 

 bringing about this result is strengthened by their mutual 

 reactions on one another. At pp. 187-139 he gives a variety 

 of examples of these mutual reactions, and says that they 

 "produce a maximum of effect which, without their aid, 

 would be altogether unattainable." 



4. As has already been shown, we both agree as to the 

 necessity of certain geographical conditions for the produc- 

 tion of' the glacial epoch. For although that epoch was 

 mainly brought about by the physical agencies, yet these 

 agencies could not have produced the required effect unless 

 the necessary geographical conditions had been supplied, 

 these being necessary for their effective operation. 





