CHAPTER YIII. 



EXAMINATION OF MR. ALFRED R. WALLACE'S MODIFICA- 

 TION OF THE PHYSICAL THEORY OF SECULAR CHANGES 

 OF CLIMATE — Continued. 



Professor J. Geikie on Condition of Europe during Interglacial 

 Periods. — Scotland during Interglacial Periods. — Difficulty in 

 Detecting the Climatic Character of the Earlier Interglacial 

 Periods. — Objection as to the Number of Interglacial Periods. 

 — Objection as to the Number of Submergences. — Interglacial 

 Periods less strongly marked in Temperate Regions than Glacial. 



II. Geological and Palceontological Facts in relation 

 to Mr. Wallace's Modification of the Theory. 



Mr. Wallace's chief, and indeed only real, modification 

 of my theory, is to the effect, as I have pointed out, that 

 the alternate phases of precession, causing the winter 

 of each hemisphere to be in aphelion and perihelion 

 each 10,500 years, would produce a complete change 

 of climate only when a country was partially snow- 

 clad. According to his view, when the greater part 

 of North-western Europe was almost wholly buried 

 under snow and ice, those glacial conditions must 

 have continued, and perhaps have even become 

 intensified, when the winter solstice moved round to 

 perihelion, instead of being replaced, as I have main- 

 tained, by an almost perpetual spring. In short, Mr. 

 Wallace's conclusion is that, during the Glacial Epoch 

 proper, a warm and equable Interglacial Period could 

 not have occurred. 



