DEDUCTION IN THE SCHEME OF THE ARID CYCLE 597 



A few examples of high-level intermont basins are known in Tibet, the 

 wet-weather drainage of which appears, from the fragmentary descrip- 

 tions now available, to have been rather recently diverted to adjoining 

 basins of lower level; but the accounts of the connecting gorges are so 

 brief, so inadequate, that it is impossible to say whether they are conse- 

 quences of spontaneous captures or not. In my own experience, the 

 nearest approach to the capture of a higher arid basin by a lower one was 

 seen in 1914 from a train on the Western Pacific Railroad about 100 

 miles west of Salt Lake City, where ascent was made through a mountain 

 notch from a lower to a higher basin floor; but much extension of the 

 gorge by headward erosion will be necessary before the whole drainage 

 of the higher basin will become tributary to the lower one. 



Unlike Use of the Cycle in Geology and Geography 



A closing paragraph may be given to the unlike use of the cycle of 

 erosion by geologists and geographers. For geologists, cycles of erosion, 

 either very brief or nearly complete, are events in the past history of the 

 earth, and as such are to be treated like any other past events. Their 

 recognition has contributed greatly to the completion of those chapters 

 of geological investigation which are concerned with the evolution of 

 land areas, by showing not only that erosion has taken place at one epoch 

 or another, but also by making it clear how far erosion proceeded in 

 each epoch. The problem of the Great Basin ranges might be here 

 reviewed to advantage, for it whs not correctly solved until the cycles 

 of erosion that it involved were explicitly recognized and defined. On 

 the other hand, for geographers — or rather for those geographers who 

 are particularly interested in the careful and intelligible description of 

 the stage-setting in which the human drama is played — the scheme of the 

 cycle of erosion has its chief value not as a means of reproducing the past, 

 but as a means of describing the present. 



In illustration of this point : If the district of Snowdon, in north 

 Wales, or of James Peak, in the Rocky Mountains front range, is 

 described by a geologist, each of the successive incomplete cycles of 

 erosion, normal and glacial, that the mountain and its district have 

 suffered deserves equal attention and all of them should be set forth 

 in historical sequence. If Snowdon or James Peak is described by a 

 geographer, its existing form should be directly stated as a consequence 

 of the successive cycles of erosion it has suffered. The sole reason for 

 such explanatory description by a geographer is, not that it gives a knowl- 

 edge of the past, but that it gives a more effective knowledge of the 



