104 GUIDEBOOK OF-THE WESTERN UNITED STATES. 
(slate or hardened shale) of the Belt series (Algonkian). “The rail- 
way follows the west base of a mountain slope of this formation for 
nearly a mile and then enters the broad valley at the junction of 
Boulder and Jefferson rivers. 
On looking back from the vicinity of Cardwell one is impressed 
with the abrupt ending of the broad valley a little east of this place, 
and the mountainous barrier that has apparently 
Cardwell. been thrown across the pathway of the stream. It 
ae aa is evident that either the mountains have risen across 
the valley, or the valley about Cardwell has been 
depressed far below its former level, or perhaps both of these move- 
ments have taken place. As the river has succeeded in cutting a 
canyon through the uplifted mass, the movement must have been 
very slow, else the stream would have been ponded and found an 
outlet in some other place. 
The valley of Jefferson River, although little above water level, is 
very fertile, and good crops are raised in the vicinity of Cardwell. 
In flowing through this flat-bottomed valley the river is not confined 
to a single channel but breaks up into a number of channels, which 
in turn branch and unite in a com- 
SSS SX SS plex and confusing manner. Such 
SOS eS a system of interlacing channels 
is called a braided stream. It is 
caused by the slight fall of the 
stream, which prevents it from carrying away all the sediment swept 
in by the numerous tributaries. This material chokes the stream and 
forces it to spread into numerots shallow and shifting channels, 
resembling the strands of a braid, as shown in figure 21. 
' Figure 21.—Diagram of braided stream. 
followed up the main river toward the southwest, whereas the North- 
