1S94-J 261 [Dodge. 
were worn fartlier and farther from the stream bed. At the 
same time tribntary streams would develop in the minor side 
depressions of the valley and would add both their volume and 
loail to the main stream. As the amount of surface furnishing 
waste to the stream gradually increased, tlie l(»ad would become 
greater ami greater until finally it exceeded the carrymg pov.er 
of the river. The waste would then be de])Osited in an alluvial 
l>lain, and the liver would have passed from its j)eriod of infancy, 
when its work is only desti'uctive, to that of adolescence when 
it does constructive as well as destructive work. 
During adolescence the river would continue to dissect the 
constructional plaui, in the manner just described, until finally 
nothing would lemain as a witness of the original plain except 
nanow divides which in places would rise to the level of their 
former elevation, and by their evenness would attest to the 
|n-evious existence of a connected plain of considerable extent. 
When the river has dissected its plain to such an extent as this, 
it is said to have attained maturity. At maturity there would be 
the greatest diversity of topography in the region, and the river 
would be doing its most effective work, for there would be the 
greatest possible amount of surlac^e exposed to erosion and the 
greatest facility for transportation. As the divides began to 
disappear in the later maturity of the river, the relief would 
gradually become less and less intense. The river would at the 
same time become enfeebled as its grade decreased and would do 
its work more slowly, until finally the whole legion would be 
almost reduced to the level of the flood plain. The river has then 
reached old age. 
If, however, the cycle of tlenudation should be interrupted by 
the elevation or depression of the land, a new cycle would be 
inaugurated. If the land should rise, the rivers would be revived 
and would again begin to cut down their channels ; if it should 
sink, the ocean waters would advance into the lower courses of 
the rivers, forming estuaries, and the rivers would be said to be 
drowned. As we have called the to|)Ography developed in one 
cycle simple, we may well call that developed in more than 
one cycle composite. 
If then alluvial river terraces should dej>end entirely for their 
formation on the development of a river system, we might ex])ect 
