318 On the Geology of the Northwestern Regions of America. 
Mountain Limestone of English geologists. From the highest 
part of the range, near latitude 55° N, where it attains an eleva- 
tion of 16,000 feet above the sea, the four largest rivers of North 
America—the Missouri, the Saskatchewan, the Mackenzie, and 
the Columbia take their rise. It may be added, that these four 
feeders of opposite oceans not only take their origin from the 
same range of mountains, but three of them almost from the 
same hill,—the head-waters of the Columbia and the Mackenzie 
being only about “two hundred yards” apart, and those of the 
Columbia and the Saskatchewan, not more than “fourteen paces.” 
It may be mentioned also as a singular fact, that one branch of 
the Mackenzie, the “ Peace River” of Sir Alexander Mackenzie, 
actually rises on the western side of the Rocky Mountains within 
300 yards of another large river flowing into the Pacific, the 
‘l'acoutchetesse, or Fraser’s River, which discharges itself into the 
Gulf of Georgia, opposite Vancouver’s Island. 
Central Plateau of Crystalline Rocks.—Marcou, in his re- 
cently published Geological Map of the United States has traced 
the crystalline formation of the Laurentine Mountains a consider- 
able distance to the westward of Lake Superior, where it appears 
to form the chief constituent of the low watershed which sepa- 
prairies on the west), until it reaches Lake Winnipeg, along 1) 
eastern side of which it is then continued for about 280 miles in 
nearly a N NW direction. From Norway Point at the north end 
of Lake Winnipeg to Isle & la Crosse, a distance of 420 miles im 
a straight line, the western boundary has, according to Sir John 
Richardson, a WNW direction. For 240 miles from Isle 4 
Crosse to Athabasca Lake, its course turns in a somewhat ! 
lar outline northward, enclosing the whole of that lake with the 
exception of its western extremity. Thence it is continued to 
