398 LAKE SUPERIOR. 



grees of longitude. Here, as in Northern Europe, the boulders 

 evidently originated farther north than their present location, and 

 have been moved universally in a main direction from north to 

 south. 



From data which are, however, rather incomplete, it can be 

 further admitted that similar phenomena occur further west across 

 the whole continent, everywhere presenting the same relations. 

 That is to say, everywhere pointing to the north as to the region of 

 the boulders, which generally disappear about latitude 38. 



Without entering at present into a full discussion of any theoreti- 

 cal views of the subject, it is plain that any theory, to be satisfactory, 

 should embrace both the extensive northern phenomena in Europe 

 and North America, and settle the relation of these phenomena to 

 the well-authenticated local phenomena of Central Europe. 



Whether America itself has its special local circumscribed cen- 

 tres of distribution or not, remains to be seen. It seems, however, 

 from a few facts observed in the White Mountains, that this chain, 

 as well as the mountains of north-eastern New York, have not been 

 exclusively and for the whole duration -of the transportation of 

 these materials under the influence of the cause which has distrib- 

 uted the erratics through such wide space over the continent of 

 North America. But whether this be the case or not, (and I 

 trust local investigations will soon settle the question,) I maintain 

 that the cause which has transported these boulders in the American 

 continent must have acted simultaneously over the whole ground 

 which these boulders cover, as they present throughout the continent 

 an uninterrupted sheet of loose materials, of the same general 

 nature, connected in the same general manner, and evidently dis- 

 persed at the same time. 



Moreover, there is no ground, at present, to doubt the simulta- 

 neous dispersion of the erratics over Northern Europe and Northern 

 America. So that the cause which transported them, whatever it 

 may be, must have acted simultaneously over the whole tract of land 

 west of the Ural Mountains, and east of the Rocky Mountains, with- 

 out assuming anything respecting Northern Asia, which has not yet 

 been studied in this respect ; that is to say, at the same time, over 

 a space embracing two hundred degrees of longitude. 



