On the Geology of the Northwestern Regions of America. 319 
MacTavish Bay in Great Bear Lake, a distance of 500 miles in a 
general direction of about NW by W, and is marked according 
to Sir John Richardson, “by the Slave River, a deep inlet on the 
horth side of Great Slave Lake, and a chain of rivers and lakes, 
including Great Marten Lake, which discharge themselves into 
that inlet.” From Great Bear Lake to the sea it follows the gen- 
eral course of the Coppermine River, its termination being marked 
by the mouth of that stream in lat. 71° 55’ N and long. 120° 30/ 
} or perhaps more correctly by Richardson’s River, a little to 
the west of it. In this part for the first time the chain rises to 
the altitude of hills, marked on the Map as the Copper Moun- 
tains, which attain in some parts a height of 800 feet above the 
of the river. The slight elevations composing the main 
Portion of the chain seldom rise, as has beeu already observed, 
much above the level of the surrounding country, giving to the 
entire range the character of a low swampy plateau of crystalline 
rocks, covered by an immense uetwork of small lakes and swamps, 
connected by narrow and tortuous channels. The low rugged 
Knolls of granite and gneiss, round which these channels wind, 
“have mostly,” says Sir John Richardson, “rounded summits, 
and they do not form continuous ridges, but are detached from 
each other by valleys of various breadth, though generally nar- 
fow and very seldom level. When the valleys are of considerable 
extent, they are almost invariably occupied by a lake, the propor- 
tion of water in this district being very great; from the top of 
the highest hill on the Hill River thirty-six lakes are said to be 
visible. The small elevation of the chain may be inferred from 
ai examination of the Map, which shows that it is crossed by 
Several rivers that rise in the Rocky Mountains, the most consid- 
erable of which are the Churchill, and the Saskatchewan or 
elson Rivers. These great streams have, for many hundred 
miles from their origin, the ordinary appearance of rivers in being 
bounded by continuous parallel banks, but on entering the primi- 
tive district, they present chains of lake-like dilatations, which 
are full of islands and have a very irregular outline. Many of 
the numerous arms of these expansions wind for miles through 
neighboring country, and the whole district bears a striking 
resemblance, in the manner in which it is intersected by water, 
to the coast of Norway aud the adjoining part of Sweden. The 
“cessive dilatations of the rivers have scarcely any current, but 
are connected with each other by one or more straits, in which 
the water-course is more or less obstructed by rocks, and the 
Stream is very turbulent and rapid. ‘The most prevalent rock in 
the chain is gneiss; but there are also granite and mica-slate, 
together with numerous beds of amphibolic rocks.” 
_ The entire length of this remarkable plateau, from Lake Supe- 
Hor to its termination on the Arctic Sea, may be estimated at 
