104 Erratics distributed by Ice. 



perate zones. This fact is as plain as the other fact, that the 

 local distribution of boulders has reference to high mountain 

 ranges, to groups of land raised above the level of the sea 

 Into heights, the temperature of which is lower than the sur- 

 rounding plains. And what is still more astonishing, the 

 extent of the local boulders, from their centre of distribution, 

 reaches levels, the mean annual temperature of which corre- 

 sponds, in a surprising manner, with the mean annual tem- 

 perature of the southern limit of the northern erratics. 



We have, therefore, in this agreement, a strong evidence 

 in favour of the view that both the phenomena of local moun- 

 tain erratics in Europe, and of northern erratics in Europe 

 and America, have probably been produced by the same 

 cause. 



The chief difficulty is in conceiving the possibility of the 

 formation of a sheet of ice sufficiently large to carry the 

 northeru erratics into their present limits of distribution ; 

 but this difficulty is greatly removed when we can trace, as 

 in the Alps, the progress of the boulders under the same 

 aspect from the glaciers now existing, down into regions 

 where they no longer exist, but where the boulders and other 

 phenomena attending their transportation shew distinctly 

 that they once existed. 



Without extending further this argumentation, I would call 

 the attention of the unprejudiced observer to the fact, that 

 those who advocate currents as the cause of the transporta- 

 tion of erratics, have, up to this day, failed to shew, in a 

 single instance, that currents can produce all the different 

 phenomena connected with the transportation of the boulders 

 which are observed everywhere in the Alps, and which are 

 still daily produced there by the small glaciers yet in exist- 

 ence. Never do we find that water leaves the boulders which 

 it carries along in regular walls of mixed materials ; nor do 

 currents anywhere produce upon the hard rocks in situ the 

 peculiar grooves and scratches which we see everywhere 

 under the glacier and within the limits of their ordinary 

 oscillations. 



Water may polish the rocks, but it nowhere leaves straight 

 scratches upon their surface ; it may furrow them, but these 



