tM Professor Agassiz on the Glacier Theory. 



proof that they have been transported under ice ; and in fact 

 this ought to be the case, because the polished rocks furnish 

 us with the proof that the sheet of ice covered nearly all the 

 summits of the Jura. 



The melting and the retreat of the ice seem to me to have 

 caused, at different times, according to the climatological cir- 

 cumstances, all those deluges, more or less extensive, of which 

 records have been sent down by tradition and history. It is 

 doubtless to these inundations that we must also attribute the 

 dislocation of a large portion of the moraines, especially of 

 those that, by their position, were not beyond the reach of the 

 currents, which, by acting on the detritus at the bottom of the 

 sheets of ice and of the glaciers, have given it, in many locali- 

 ties, a stratified appearance ; so much so indeed, that we might 

 be deceived as to the origin of these detrital matters, and attri- 

 bute their rounded form to the effects of great currents, as has 

 often been erroneously done. I do not believe that I deceive 

 myself when I aflftrm, that whenever rounded blocks, lying in 

 accumulations of gravel, stratified or unstratified, are scratched 

 by long rectilinear striae, their aspect is due to the action of 

 the rubbing of glaciers against their beds ; and that currents, 

 in acting subsequently on these same matters and rolling them, 

 could not but cause these characteristic marks to disappear by 

 the friction, I therefore regard the rarity of scratched peb- 

 bles and blocks, in a deposit of stratified gravel, as a proof 

 of a longer transport by water, and their total absence as a 

 proof of an action due exclusively to currents ; whereas, the 

 complete absence of stratification in the accumulations of 

 gravel and blocks uniformly rounded and scratched, seems 

 to me to be the exclusive effect of glaciers. Lastly, these cha- 

 racters may be combined when such accumulations are the com- 

 bined effect of the two causes, as may have been the case on 

 maritime shores, where the glaciers of neighbouring moun- 

 tains terminated at the coast. It must likewise not be for- 

 gotten, that sometimes small lakes are formed on the flanks of 

 glaciers, in which the matters triturated by the glacier are de- 

 posited in regular beds, without being carried very far. It is 

 pf consequence to keep all these facts in view, whea we study 



