LINEAMENTS OF THE DESERT 



21 



The second great geographic principle, that of the verity of a dis- 

 tinctly staged cycle of erosion comparable in a way to the periods of 

 growth in the human individual, has done more than anything else to 

 advance and place the study of geography on a tinily genetic basis. 

 It is to Davis we are chiefly indebted for devising for us a practical 

 working scheme. 



What the base-level of erosion is to the general theory of land 

 degradation under conditions of a normal moist climate Passarge's 

 great deduction of the possibility of general land leveling and lowering 

 without regard to sea-level is to land sculpture under conditions of a 

 dry climate. Until within the last lustrum the lineaments of the 

 great desert regions of our globe have remained without adequate or 

 satisfactory explanation. The genesis of the grander features of the 

 landscape on the basis of ordinary tectonics, or of normal erosion dur- 

 ing former wet climatic periods, or of water-action under present con- 

 ditions, has always met with seemingly unsurmouutable obstacles. The 

 origin of the salient features of the desert, its peculiar mountains, its 

 smooth plains, its strange plateaus, its streamless surface, its remark- 

 able rock-floor, and its many other unexpected features, are only begin- 

 ning to be fully appreciated in their proper relationships. To us of 

 the moister countries they present many novelties. They make us 

 acquainted with the vigorous workings of geologic processes to which 

 we are as yet almost complete strangers. 



In the operations of the geologic processes under conditions of an 

 arid climate the most noteworthy efl^ects as compared with those under 

 normal conditions are the prevalency, the constancy and efficiency of 



Ghost-like Desekt Range of Baboquivaei, Arizona. Central Peak is nearly a 

 mile high and ten miles distant. (W J McGee, photo.) 



