SOURCES OF THREE GREAT RIVER SYSTEMS. 175 



with a, considerable degree of parallelism to each other 

 before they fall into Hudson's Bay.* 



The peculiar configuration of the continent which I 

 have endeavoured to sketch must be duly considered by 

 any one who endeavours to detect the agency by which 

 the river valleys and lake basins were excavated. It is 

 not, however, my purpose to enter upon the discussion 

 of this question, or to speak of the partial and often 

 repeated elevations and depressions by which the lacustrine 

 and fluviatile terraces have been accounted for ; nor would 

 a summary of this kind admit of the necessary elucidations. 

 I shall merely say that, adopting the opinion of the United 

 States' geologists, that they are basins of excavation, I 

 consider them all to be of the same epoch, and that the 

 currents or waves of translation, if such they were, must 

 have had an easterly direction in the middle latitudes, and 

 gained strength as they rolled towards the Atlantic, when 

 they swept away wholly or partially the fossiliferous de- 

 posits that once covered the primitive rocks of Hudson's 

 Bay, Canada, and the eastern parts of the United States ; 

 the former extent of the newer rocks being indicated by 

 the patches which remain. By a singular coincidence of a 

 political with a natural limit, the northern boundary of the 

 United States, or the 49th parallel, marks the line on the 

 great prairie slope, where the current took a southerly 

 direction, to excavate the wide and magnificent valley of 

 the Mississippi. A similar diversion of the excavating 



* A study of the map will show, that the lake basins north of the 

 St. Lawrence have generally their long axes across the river courses 

 to which they respectively belong, and that many assume a greater 

 or less degree of parallelism to the intermediate primitive belt. Per- 

 haps movements of elevation or depression had occasioned an exten- 

 sive disruption of strata along the western border of the hypogene 

 rocks, previous to the removal of the silurian beds on the excavation 

 of the lake valleys. 



