82 National Geographic Magazine. 
The generalizations here referred to may be presented in the 
form of a classification, following the ideas of Powell, Gilbert, 
Heim, Léwl and others, as follows : 
Oonsequent rivers.—Those that, have in their birth, at the time 
of their original establishment on the country which they drain, 
selected courses 1n accordance with the constructional slopes of 
the surface ; for example, the Red River of the North and such 
of its branches as flow on the even surface of the lacustrine plain 
of Lake Agassiz; the several streams that drain the broken lava 
blocks of Southern Oregon; certain streams and rivers of the 
Jura that drain the synclinal troughs of those mountains. Con- 
sequent streams may be divided into definite and indefinite 
groups. Definite consequent streams are those that follow well 
defined constructional channels, such as the axial line of a syn- 
clinal trough, or the lowest point of an anticlinal arch between 
two synclinal basins ; they are defined in location as well as in 
direction. Indefinite consequent streams are those that flow down 
constructional slopes, such as the flanks of an anticline, but whose 
precise location depends on those minor inequalities of surface 
that we term accidental ; they are defined in direction but not in 
location ; and they are as a rule branches of definite consequent 
streams. i 
Antecedent rivers.—Those that during and for a time after a 
disturbance of their drainage area maintain the courses that they 
had taken before the disturbance. In Powell’s original definition 
of this class of rivers, he said that the valleys of the Uinta 
mountains are occupied by “drainage that was established ante- 
cedent to the corrugation or displacement of the beds by faulting 
or folding.”* No limit is set to the amount of corrugation or 
displacement or to the strength of the faulting or folding. It 
therefore seems advisable to consider what variations there may 
be from the strongly marked antecedent type ; one extreme being 
in those cases where the displacement was a minimum and the 
perseverance of the streams a maximum, the other where the dis- 
placement was.a maximum and the successful perseverance of the 
streams a minimum, or zero. The simplest examples of antece- 
dent rivers are therefore found in regions that have been broadly 
elevated with the gentlest changes of slope, so as to enter a new 
cycle of topographic development, all the streams retaining their 
previous courses, but gaining ability to deepen their former chan- 
* Colorado river of the West, 163. 
