128 Mr. J. Croll on the Physical Cause of the 



for example, that the eold of the glacial epoch might result 

 from the absence of the Gulf-stream during that period. 



Mr. Hopkins calculates that the absence of the Gulf -stream 

 would lower the mean temperature of January 24° F. in the 

 north of Scotland, but could have no sensible influence on the 

 July temperature of London, or places in western Europe further 

 to the south*. 



Mean annual temperature due to the Gulf- stream. 



Iceland 18 F. 



North of Scotland . . . 1225 



Snowdon 7*5 



Alps 3 



Were the indications of ancient glaciers confined to the 

 western parts of Europe, the absence of the Gulf-stream might 

 to a considerable extent account for the phenomena of the glacial 

 period. But we know that the glaciation extended over the 

 greater part of northern Europe and northern America. It is 

 perfectly evident that the absence of the Gulf-stream in our seas 

 could not, for example, greatly lower the temperature of the 

 climate of North America. Neither would a decrease of 3° F. 

 in the mean annual temperature of the Alps, account for the 

 enormous glaciers which we know existed there during that 

 period. 



Sir Charles Lyell supposes that, were the land all collected 

 round the poles while the equatorial zones were occupied by the 

 ocean, the temperature of the climate would be lowered to an 

 extent that would account for the glacial epoch. And on the 

 other hand, were the land all collected along the equator, while 

 the poles were covered with sea, a temperature such as existed 

 during the coal-period might be produced. Professor Phillips 

 admits that if the land were all collected round the poles, the 

 temperature of the globe would be lowered ; but he remarks, 

 truly, that this supposition does not agree with the observed 

 facts regarding the glacial deposits, for these require deep sea 

 over much of what is now in circum polar zones. Professor 

 Phillips appears to doubt very much whether the collecting of 

 the land along the equator would sensibly increase the tempera- 

 ture of the globe ; but suggests that the rise of temperature 

 might result from the land being divided into" low islands scat- 

 tered over the area of the globe, amidst large breadths of water. 

 But he brings forward no geological evidence in favour of such 

 a state of distribution of land and sea during the warm epochs. 

 It is perfectly evident that if the great changes of climate 



* Journal of the Geological Society, vol. viii. 



