The Glacial Theory. 



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rough surfaces, just like the blocks of the moraines of the glaciers of 

 the present day. Foreign blocks, whose origin is not British, and 

 which were doubtless transported on the surface of the great sheet 

 of ice, or on rafts of ice at the period of its dissolution, ought to be 

 angular, and, for the most part, are so in reality. In this way, the 

 form of erratic blocks implies, in some degree, at first sight, their 

 mode of transport. I am able to add, as a confirmation of what I 

 have said as to the form of the erratic blocks of Scotland, that the 

 blocks of the Jurassic rocks, which we meet with in the diluvium of 

 the interior valleys of the Jura, are all rounded ; a 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 circumstances, all 

 those deluges, more or less extensive, of which records have been 

 sent down by tradition and history. It is doubtless to these inun- 

 dations 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 localities, a stratified appearance ; so much so indeed, that 

 we might be deceived as to the origin of these detrital matters, and 

 attribute 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 affirm, that whenever rounded blocks, lying in accumulations 

 of gravel, stratified or unstratified, or 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 character- 

 istic marks to disappear by the friction. I therefore regard the 

 rarity of scratched pebbles 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 accumulations of gravel and 

 blocks uniformly rounded and scratched, seems to me to be the ex- 

 clusive effect of glaciers. Lastly, these characters may be combined 



