12 A Mr. J. Croll on the Physical Cause of the 



cold body. Astronomical science affords not the slightest evi- 

 dence in favour of such an hypothesis *. 



A theory has lately been propounded by Prof. Franklandf, 

 wherein the changes of climate experienced by our earth during 

 past epochs is referred to a difference in the influence of internal 

 heat on the sea and on land. He concludes that the cooling of the 

 floor of the ocean would not proceed so rapidly as if it had been 

 freely exposed to the air. And hence it would continue at a 

 comparatively high temperature long after the surface of the 

 dry land had reached its present mean temperature. And as 

 heat is transmitted from the bottom to the surface of the ocean, 

 not by conduction, but by convection, viz. by the warm stratum 

 of water in contact with the bottom rising to the surface, the 

 temperature of the ocean would consequently be higher than 

 the mean temperature of the earth's surface. He concludes 

 that this state of things satisfactorily accounts for the glacial 

 epoch. " The sole cause of the phenomena of the glacial epoch," 

 he says, "was a higher temperature of the ocean than that 

 which obtains at present." 



The high temperature of the ocean, he believes, would give 

 rise to augmented atmospheric precipitation. This would pro- 

 duce such an accumulation of snow during winter months as 

 would defy the heat of summer to melt. The overcast sky 

 during summer, caused by the great amount of evaporation, 

 would intercept the sun's rays, and thus reduce the summer's 

 temperature. 



While admitting the general correctness of Prof. Frankland's 

 theory, we, however, fear that it does not altogether harmonize 

 with the facts of geology. There is no evidence to support the 

 conclusion that the ocean was warmer during the glacial epoch 

 than at present; but, on the contrary, we have geological 

 evidence to conclude that it must have been much colder than 

 at present. For example, on examining the fauna of the marine 

 drift of that period, we find that it is decidedly of an arctic cha- 

 racter, indicating the low temperature of the seas during that 

 epoch. These beds show, for example, that our British seas 

 during that period contained in abundance numerous species of 

 shells which are now only to be found in more northern lati- 

 tudes J. In the glacial drift of Scotland alone there have been 

 found the following species of an arctic character, and which are 



* See Mr. Hopkins's remarks on this theory, Journal of the Geological 

 Society, vol. viii. 



t Phil. Mag. for May 1864. 



% This important fact was first noticed by Mr. Smith of Jordan Hill, 

 and communicated to the Wernerian Society in the early part of 1839. 

 See his Collected Papers published by John Gray, Glasgow. 



