LETTER FROM LONGFELLOW. 665 



lisliecl ? We can no longer evade the ques- 

 tion by supposing these phenomena to be due 

 to the action of great currents. We have to 



c? 



do first with sheets of ice, five or six thousand 

 feet in thickness (an estimate which can be 

 tested by indirect measurements in the North- 

 ern States), covering the whole continent, and 

 then with the great currents which ensued 

 upon the breaking up of that mass of ice. 

 He who does not distinguish between these 



o 



two series of facts, and perceive their connec- 

 tion, does not understand the geology of the 

 Quaternary epoch. . . . 



Of about this date is the following pleasant 

 letter from Longfellow to Agassiz. Although 

 it has no special bearing upon what precedes, 

 it is inserted here, because their near neigh- 

 borhood and constant personal intercourse, 

 both at Cambridge and Nahant, made letters 

 rare between them. Friends who see each 

 other so often are infrequent correspondents. 



ROME, December 31, 1868. 



MY DEAR AGASSIZ, I fully intended to 

 write you from Switzerland, that my letter 

 might come to you like a waft of cool air 

 from a glacier in the heat of summer. But 



