356 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9. 



site hemisphere after half that interval, or 12,500 years. Now no 

 geological evidence could detect an interval of 12,500 years between 

 the dates of glacial scratches or of beds of drift in widely separated 

 regions, such as Scotland and Patagonia. But according to M. Mar- 

 tins there is geological evidence of at least two glacial periods, with 

 a geologically short interval between them ; and such recurrent 

 glacial periods ought to be expected on either Mr. CroU's theory or 

 mine. 



It is to be observed, in conclusion, that Mr. CrolFs reasoning and 

 mine leave untouched the arguments by which Sir Charles Lyell 

 has endeavoured to show how all changes of climate may be referred 

 to geographical causes, especially to changes in the distribution of 

 land and water, and changes in the direction of the ocean- currents 

 produced by these. The chmate of any region at any period is due 

 to a complication of causes, some of which are geographical, and 

 some astronomical. Sir Charles Lyell has dealt with the geogra- 

 phical ones, Mr. Croll and I with the astronomical ones. There is 

 no doubt that the geographical causes of changes of climate are 

 verm causae, ; but it is not so certain that they are fully adequate to 

 account for the facts. It is equally certain that the astronomical 

 causes also are veroe. causce ; and I have endeavoured to show what 

 their mode of operation must be. 



Discussion. 



Prof. Ramsay remarked that Prof. Dana and himself had both 

 referred the origin of many fjords to the same cause as the author. 



