154 



ISLAND LIFE. 



[part T. 



off the sun-heat, and then snow falls even during summer, and 

 the stored-up cold does not diminish during the year. When, 

 however,only a small portion of the surface is covered with ice, 

 the exposed earth becomes heated by the hot sun, this warms 

 the air, and the warm air melts the adjacent ice. It follows, 

 that towards the equatorial limits of a glaciated country 

 alternations of climate may occur during a period of high ex- 

 centricity, while nearer the pole, where the whole country is 

 completely ice-clad, no amelioration may take place. Exactly 

 the same thing will occur inversely with mild Arctic climates; but 

 this is a subject which will be discussed in the next chapter. 



This view of the character of the last glacial epoch strictly 

 corresponds with the facts adduced by geologists. The inter- 

 glacial deposits never exhibit any indication of a climate whose 

 warmth corresponded to the severity of the preceding cold, 

 but rather of a partial amelioration of that cold ; while it is only 

 the very latest of them, which we may suppose to have occurred 

 when the excentricity was considerably diminished, that exhibit 

 any indications of a climate at all warmer than that which now 

 prevails.^ 



.1 In a recent number of the Geological Magazine {A^rU, 1880) Mr. Searles 

 V. Wood adduces what he considers to be the " conclasive objection" to 

 Dr. Croll's excentricity theory, which is, that during the last glacial epoch 

 Europe and North America were glaciated very much in proportion to 

 their respective climates now, which are generally admitted to be due to 

 the distribution of oceanic currents. But Dr. Croll admits his theory to 

 be baseless unless there was a complete diversion of the warm ocean 

 currents from the hemisphere glaciated," in which case there ought to be 

 no difference in the extent of glaciation in Europe and North America. 

 Whether or not this is a correct statement of Dr. CrolPs theory, the above 

 objection certainly does not apply to the views here advocated ; but as I 

 also hold the " excentricity theory " in a modified form, it may be as well to 

 show why it does not apply. In the first place I do not believe that the 

 Gulf Stream was ^'completely diverted" during the glacial epoch, but 

 that it was diminished in force, and (as described ^t p. \Zd>) partly diverted 

 southward. A portion of its influence would, however, still remain to 

 cause a difference between the climates of the two sides of the Atlantic ; 

 and to this must be added two other causes — the far greater penetration 

 of warm sea-water into the European than into the North American conti- 

 nent, and the proximity to America of the enormous ice-producing mass 

 of Greenland. We have thus three distinct causes, all combining to 



