382 Mr. J. Croll on Geological Time, and the iwohable 



entire country is covered with snow and ice. The trunk of a 

 white spruce tree was dug up by Sir E. Belcher near Wellington 

 Sound, in lat. 75° 32' N. The remains of an ancient forest were 

 discovered by Captain M'Clure in Bank's Land in lat. 74° 48'. 

 "This remarkable phenomenon/' says Captain M'Clure, "opens 

 a vast field for conjecture; and the imagination becomes bewil- 

 dered in trying to realize that period in the world's history, 

 when the absence of ice and a milder climate allowed forest- 

 trees to grow in a region where now the ground-willow and 

 dwarf-birch have to struggle for existence." Evidence of ancient 

 forests was found in Prince Patrick's Island and in Melville 

 Island, one of the coldest spots, perhaps, in the northern hemi- 

 sphere. 



These phenomena have excited a very great amount of asto- 

 nishment, and have been considered very puzzling ; but they 

 need not be so regarded if it be the case that the climate of the 

 globe is greatly affected by variations in the excentricity of its 

 orbit ; for in such a case there could not possibly be a glacial 

 epoch extending over a long course of time without the frequent 

 recurrence of warm periods. From geological evidence alone, 

 independently of cosmical considerations, we are warranted by 

 analogy from the Posttertiary period to expect the existence of 

 a glacial condition of things during the Upper-Miocene and 

 Middle-Eocene period, from the fact that a warm condition of 

 climate prevailed in Europe and extended to high latitudes du- 

 ring a part of those periods, similar to what we know occurred in 

 the Posttertiary period. 



The occurrence of a warm condition of climate always along 

 with a cold condition shows that the two are in some way or 

 other physically connected, and that they are both related to a 

 common cause. 



At one time I was under the impression that when the excen- 

 tricity was near to its superior limit and the winter solstice in 

 the perihelion, the mean annual temperature would not in the 

 temperate regions be higher than it is at the present day, although 

 in all probability at that time the winters Would be as warm as 

 the summers, the effect of this condition of things being to 

 produce what Sir John Herschel has called a " perpetual spring." 

 But after making calculations regarding the amount of energy 

 in the form of heat that is being continually transferred from 

 the tropical regions to the temperate and polar regions by ocean- 

 currents, and to what extent the increase in the volume of 

 those currents, which would result from that condition of things, 

 would affect the climate, I felt persuaded that that opinion 

 must be abandoned, and that a " perpetual summer " would 

 better represent the condition of climate which must then prevail. 



