of Secular Changes of Climate. 107 



solstice was in aphelion, and the condition of things is exactly 

 what, according to theory, we ought to expect. 



Preceding the period of the Carse- clays comes that of the 

 buried Forest, when the climate was even more genial and 

 equable than at the present day, the Gulf-stream larger and the 

 sea at a lower level than now. Now during this period the 

 winter solstice was in perihelion and the eccentricity some- 

 what greater than at present; and here again we have exactly 

 that condition of things which, according to theory, we ought 

 to expect. It would be very singular indeed were there no 

 physical connexion between these conditions and the causes 

 to which I have been attributing them. It would certainly 

 be singular were all these coincidences purely accidental. 

 These changes have all been so recent, geologically speaking, 

 and so general and widespread in their character, that they 

 cannot reasonably be attributed to any known geographical 

 changes. If we admit, then, that they were the result of 

 those astronomical and physical agents to which I have 

 referred them, we must also admit that those agents were as 

 efficient in producing a warm and equable climate as in pro- 

 ducing a cold and severe one. We must further admit that, 

 with a very small amount of eccentricity, widely marked 

 differences of climatic conditions are brought about on the 

 two hemispheres; that, when the winters are in perihelion, 

 the melting of the snow and ice and the increase of the 

 Gulf-stream and other northward-flowing currents are as 

 necessary a result as were the formation of the snow and ice 

 and the decrease of the Gulf-stream and those currents when 

 the winters were in aphelion. And if this holds true in refer- 

 ence to recent and postglacial times, when the eccentricity 

 was small, it must, for reasons which will presently be stated, 

 hold true in a higher degree in reference to the glacial epoch, 

 when the eccentricity was more than three times its present 

 value, 



The Mutual Reaction of the Physical Agents in relation to the 

 Melting of the Ice. — When the winter solstice is in aphelion it 

 sets in operation, according to theory, as has been shown, a 

 host of physical causes the tendency of which is to produce an 

 accumulation of snow and ice ; but when the solstice-point 

 moves round to perihelion the tendency of these causes is 

 reversed, and they then undo what they had previously done — 

 they melt the snow and ice which they had just produced. 

 The action of the causes being reversed, the effects are reversed. 

 Bat it must be observed that the greater the amount of the 

 eccentricity, the greater will be the effect resulting from the 

 combination of these physical agents, whether that effect be 



