The C linoplains of the Rio (rrande. — Herriv.k. 379 
This plane surface is broken by arroyos and base-leveling from 
the present flood plain level, but (jthcrwise the network of 
erosive channels is very intricate though shallow. A very 
good ilustration is here afforded of degradation of soft and 
homogeneous materials exactly as required by the theory of 
peneplanation . The law is simply this: "Whenever the angle 
of slope of the ridges betzveen the radial channels becomes 
greater than that of the channels themselves, erosion is more 
rapid laterally than radially, so that the general level is auto- 
matically preserved zvithin narrozv limits." 
It is certain that the high winds assist in this generalizing 
or equalizing effcci . Were the strata harder, the law would 
not hold, for perpendicular walls of the radial channels \^'ould 
be exempt from, the operation of this equalizing effect. 
The clinoplains are not all of the same hight, even in the 
same district, but they vary with the distance from the bound- 
ing mountains to liie flood plain and the nature of the materia!. 
Two methods of clinoplain fomiation may be noted . Aside 
from that just suggested, where the levelling goes on cotem- 
poraneously with the supply of material from the talus above, 
there are 'cases where the clinoplain is obviously derived from 
the confluence of deltas debouching on the flood plain and 
working over the materials of earlier clinoplains. This base- 
leveling continues till the talus is reached and then the general 
law of distribution again maintains. 
One remarkable source of material furnished the clinoplains 
in the Rio Grande valley through the mediation of the Ter- 
tiary deposits, may be noticed. Although the phenomena are 
widely distributed we will select a single illustration. 
The Limitar range, elsewhere described, which lies a few 
miles north of Socorro, has an axis of andesyte covered with 
rhylote flows. The north end of the range extends into ridges 
of rhyloyte divergmg to embrace a very irregular area which 
was evidently at one time the theatre of an intense explosive 
activity. A vast mass of volcanic breccia and tuff conglomer- 
ate is surrounded by what the writer has called "talus con- 
glomerate," the materials of which consist of rounded, water- 
worn fragments of rhyolyte in a small fine-grained cement of 
the same. Still outside, the stratification becomes more defi- 
nite and the beds are alternating tuff and coarser conglomerate. 
