400 LAKE SUPERIOR. 



there was any geographical limitation to the supposed northern 

 current to cause it to leave the northern erratics of Europe in such 

 regular order, with a constant bearing from north to south, and to 

 form, on its southern termination, a wide, regular zone from Asia to 

 the western shores of Europe, north of the fiftieth degree of lati- 

 tude, before it had reached the great barrier of the Alps ? I ask 

 whether there was such a barrier in the unlimited plains which 

 stretch from the Arctic seas uninterrupted over the whole northern 

 continent of America as far down as the Gulf of Mexico ? 



I ask, again, why the erratics are circumscribed within the north- 

 ern limits of the temperate zone, if their transportation is owing to 

 the action of water currents ? Does not, on the contrary, this most 

 surprising limit within the artic and northern temperate zones, and 

 in the same manner within the antarctic and southern temperate 

 zones, distinctly show that the cause of transportation is connected 

 with the temperature or climate of the countries over which the 

 phenomena were produced. If it were otherwise, why are there no 

 systems of erratics with an east and west bearing, or in the main di- 

 rection of the most extensive currents flowing at present over the 

 surface of our globe ? 



It is a matter of fact, of undeniable fact, for which the theory 

 has to account, that in the two hemispheres the erratics have direct 

 reference to the polar regions, and are circumscribed within the 

 arctics and the colder part of the temperate zone. 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 surrounding 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 corresponds 

 in a surprising manner with the mean annual temperature of the 

 southern limit of the northern erratics. 



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

 of the view that both the phenomena of local mountain 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 



