BVOLUTIOif OF THE CANDID. 
121 
time. The volcanism ceased to be active. The river sought and quickly 
found a new base-level at the horizon of the great esplanade of the 
Grand Canon. In its turn the process of corrasion rested. The pro- 
cess of erosion during this second period of base-level was occupied 
in the only work possible under the circumstances, viz, sapping the newly- 
formed cliffs of the canon. The cliffs, thus attacked, receded away from 
the river, gradually developing the broad avenue of the outer chasm. In 
die very few tributaries which survived the advent of the arid climate the 
same process of sapping and recession of cliffs is discernible. When the 
cliffs of the outer chasm had receded from two to three miles away from 
the river, another and more active period of upheaval set in. Again the 
country was hoisted, this time more than before. At once the corrasion of 
the river bed was renewed. The faults were increased. The volcanic fires 
were rekindled. Swiftly the inner gorge was scoured out, and the chasm 
assumed its present condition. At pi’esent the uplifting force is inactive, 
the volcanoes are extinct, the faults are not increasing, and the river has 
nearly but not quite reached another base-level. 
Throughout the entire stretch of the Grand and Marble canons this 
order of events is betrayed. It is not confined to the Uinkaret and Toro- 
weap, but is general for the whole district. The theory fits the facts per- 
fectly, and the range of facts to which it is adapted is a very wide and 
complex one ; for it comprises the drainage, the surface topography, the 
erosion, the volcanism, the displacements, the climate. All these facts and 
their respective trains of jjhenomena the theory brings into harmony, and 
it shows their relations to each other. In the following chapters the same 
grouping of the facts in a systematic process of evolution will appear again 
and again until the cumulative proof becomes irresistible. 
