ON ITS EXTERIOR. VOLCANOES. 427 



minerals, whose varied, yet often repeated association is 

 the result of volcanic activity. He has, partly out of 

 kindness to myself, and at my solicitation, particularly 

 since 1834, repeatedly examined the specimens which I 

 brought back with me from the volcanoes of New Gra- 

 nada, Los Pastos, Quito, and the high land of Mexico, 

 and has compared them with those brought from other 

 parts of the world, which are contained in the rich 

 mineralogical collection of Berlin. Leopold von Buch, 

 when he was in Paris, in 1810 1811, between his re- 

 turn from Norway and his departure for Teneriffe, at a 

 time when my collections had not been separated from 

 those of my companion, Aime Bonpland, had examined 

 them microscopically with persevering diligence. He 

 had also previously, while with Gray-Lussac in Rome, in 

 the summer of 1805, and afterwards in France, taken 

 into consideration what I had written down at the time 

 and on the spot, in my travelling journal, both respect- 

 ing particular volcanoes and in general (in July 1802) 

 " Sur 1'affinite entre les volcans et certains porphyres 

 depourvus de quartz."( 590 ) I preserve, as a valued me- 

 morial, some pages with remarks on the volcanic pro- 

 ducts of Quito and Mexico, which that great geologist 

 wrote for my information more than 46 years ago. 

 Since, as I have elsewhere explained more circumstan- 

 tially ( 591 ), travellers can but carry forward the incom- 

 plete knowledge of their own time, and their observations 

 are liable to be deficient in many of the guiding ideas 

 and of the distinguishing marks which are the fruits of 

 progressive knowledge, a time may arrive when the 

 materials they have collected and arranged geographi- 

 cally will almost alone retain a value. 



