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g K_SIT Yn 



MECHANICAL ACTION OF GLACIERS. 147 



withdrawn ; and ice is elastic, as elastic, apparently, as is 

 glass. But there is also another phase~oT^he same pheno- 

 menon which presents itself. It is alleged, and it has 

 been satisfactorily demonstrated, that in the course of 

 passage through a narrow strait or over a steep precipice, 

 a sheet of ice becomes broken up into an infinite number 

 of small pieces, admitting thus of an easy passage of the 

 mass ; and that these become frozen together again on 

 their escape from the pressure. And thus, like the 

 tenacious substances which have been named, honey and 

 tar, the ice flows on in an apparently solid, as do these in 

 a semifluid form or consistence. 



But in doing so the friction on the bottom and sides of 

 the channel is great, In many places I had almost said 

 in all countries in these northern latitudes, including our 

 own there may be seen hard rocks on mountain sides, 

 and in some cases on mountain tops, marked with striae, 

 fine parallel hairstrokes, which are attributed to the 

 passage of ice in a state of flux. Besides these there are 

 found everywhere what are called boulders large masses 

 of rock, which have been torn from sides of mountains by 

 passing glaciers, borne along by the moving stream, em- 

 bodied in it it may be, and deposited where the ice melt- 

 ing could no longer sustain it. On the surface of the 

 glacier, moreover, there are often seen longitudinal streaks 

 of debris which have fallen upon it from higher situated 

 mountain sides as the glacier passed. Moraines, linear 

 deposits of stones and rubbish across valleys, are the pro- 

 duce of such, carried down to the lower edge of the glacier, 

 and dropt as this melted away through the heat. In 

 some valleys there are a succession of such moraines, 

 separated by greater or less distances. These indicate 

 what had at successive periods been the extremity of a 

 glacier previously existing there, which extremity in exist- 

 ing glaciers may be shown to have alternately receded and 

 advanced, and again, it may be, receded and again ad- 

 vanced, only again to recede, after more or less protracted 

 periods of stationary limit, according as the local tempera- 



