xv.] FORBES' GLACIER DISCOVERIES. 499 



adopted on equally valueless evidence ; rendering it 

 absolutely necessary to any real progress in the subject, 

 that, as a preliminary, facts should be carefully ascer- 

 tained. The following extract from Forbes' work (Travels, 

 }>}). 33-38) will give a clear notion of the state of affairs 

 when he took up the subject : 



* The theory which appears at first sight most readily 

 to account for the leading facts, is that maintained 

 by De Saussure, that the valleys in which glaciers lie 

 being always inclined, their weight is sufficient to 

 urge them down the slope, pressed on by the accumu- 

 iis of the winter snows above, and having their 

 sliding progress assisted by the fusion of the ice in 

 contact with the ground, resulting from the natural 

 li -at of the earth. 1 



'Tliis cause of motion has been rejected as insufficient 

 by M. de Charpentier, who has supported another, which 

 (though like the last, suggested originally by an older 

 author, Scheuchzer, as De Saussure's was by Gruner), 

 having received a scientific form and detail in his hands, 

 /ill call " Charpentier's Theory of Dilatation," as the 

 other may be called " Saussure's Gravitation Theory," or 

 the sliding theory. 



'De Charpentier's theory is this: The snow is pene- 

 trated by water and gradually consolidated. It remains, 

 however, even in the state of ice, always permeable to 

 water, by means of innumerable fissures which traverse the 

 mass ; these are filled with fluid water during the heat 



1 ' I wish to quote De Saussure's own statement of his views, which 

 is very distinct : " Ces masses glac6es entralnees par la pente du 

 f-Mi-1 sur lequel elles reposent, degagees par les eaux de la liaison 

 <l'.iVUes ppurraient contractor avec ce meme fond, soulev^es memo 

 (juelquefois par les eaux, doivent peu-a-peu glisser et descendre en 

 Buivant la pente des vallees ou des croupes qu'elles couvrent. C'est 

 ce glissement lent, mais continu, des glaces sur leurs bases inclines, 

 cjui lus entraine j usque dans les basses valleos, etquientretimt o.ntinu 

 ellement des amas de glaces dans les vallons assezchauds pour produiro 

 de grands arbrea, et mfime de riches moissons." Voyage*, T> 

 De Saussure's very clear views respecting the action of the heat of the 

 earth, see 532535, 739, &c.' 



