ANNOTATIONS AND ADDITIONS. 51 



low plain or basin of the Mississipi, the greater part of which 

 is from 400 to 600 French feet above the level of the sea, 

 or about twice the elevation of the plains of Lombardy. 

 The hypsometric conformation of this eastern region, i. e. the 

 altitude of its several parts above the sea, has been elucidated 

 by the valuable labours of the highly-talented Trench astro- 

 nomer, Nicollet, of whom science has been deprived by a 

 too early death. His large and excellent map of the Upper 

 Mississipi, constructed in the years 1836-1840, is based on 

 240 astronomically determined latitudes, and 170 barometric 

 measurements of elevation. The plain which contains the 

 basin of the Mississipi is one with the Northern Canadian 

 plain, so that one low region extends from the Gulf of 

 Mexico to the Arctic Sea. (Compare my Relation Histo- 

 rique T. iii. p. 284, and Nicollet's Report to the Senate of 

 the United States, 1843, p. 7 and 57.) Where the plain is 

 undulating, and where, between 47 and 48 of latitude, low 

 hills (coteaux des prairies, and coteaux des bois, in the still 

 un-English nomenclature of the natives) occur in connected 

 ranges, these ranges and gentle swellings of the ground 

 divide the waters which flow towards Hudson's Bay from 

 those which seek the Gulf of Mexico. Such a dividing line 

 is formed north of Lake Superior by the Missabay Heights, 

 and more to the west by the " Hauteurs des Terres," in 

 which were first discovered, in 1832, the true sources of the 

 Mississipi, one of the largest rivers in the world. The 

 highest of these ranges of hills hardly attains an elevation 

 of 1400 to 1500 (1492 to 1599 English) feet. From 

 St. Louis, a little to the south of the junction of the Mis- 



