LETTER TO HIS MOTHER. 639 



summary of this delightful journey may close 

 as it began with a letter to his mother. 



o 



AT SEA, July 7, 1866. 



DEAR MOTHER, When you receive this 

 letter we shall be, I hope, at Nahant, where 

 our children and grandchildren are waiting 

 for us. To-morrow we shall stop at Pernam- 

 buco, where I shall mail my letter to you by 

 a French steamer. 



I leave Brazil with great regret. I have 

 passed nearly sixteen months in the uninter- 

 rupted enjoyment of this incomparable trop- 

 ical nature, and I have learned many things 

 which have enlarged my range of thought, 

 both concerning organized beings and con- 

 cerning the structure of the earth. I have 



o 



found traces of glaciers under this burning 

 sky ; a proof that our earth has undergone 

 changes of temperature more considerable than 

 even our most advanced glacialists have dared 

 to suggest. Imagine, if you can, floating ice 

 under the equator, such as now exists on the 

 coasts of Greenland, and you will probably 

 have an approximate idea of the aspect of the 

 Atlantic Ocean at that epoch. 



It is, however, in the basin of the Amazons es- 

 pecially, that my researches have been crowned 



