190 ADDEESS. [lect. vi. 



far colder than now, then for a similar period far hotter, 

 then far colder again, and so on for several variations. 

 These alternations of hot and cold periods beautifully 

 explain the difficult problem of how to account for the 

 existence of remains belonging to tropical and to arctic 

 animals, associated together in the same river gravels. 

 It also throws light on the fact, first pointed out by my 

 friend M. Morlot, that there are in Switzerland geolo- 

 gical indications of several periods of extreme cold, with 

 others of more genial climate, and Mr. Croll in his Cli- 

 mate and Time, has pointed out, from the evidence of 

 250 borings in the Scotch glacial beds, that many of 

 them show evidence of the existence of warm inter- 

 glacial periods. 



The antiquity of this period, therefore, really must be 

 solved by the mathematician and physicist, rather than 

 by the antiquary, and it affords us an excellent illustra- 

 tion of the manner in which the different branches of 

 science depend upon one another, and of the fact that 

 the more science advances, the more necessary it is 

 that our higher education should be based on a wide 

 foundation. 



