236 CHARLES KEYES 



somewhat above the tops of the present mountains. Inasmuch as 

 desert conditions began to set in about the same time, there is 

 every reason to beheve that the magnitude of the general land 

 depletion is represented by the difference between this old pene- 

 plain level and the present plains level — an interval of between 

 5,000 and 6,000 feet — or something over one mile of thickness, 

 over an area equal to nearly one-quarter of that of the entire 

 United States. 



There are many considerations supporting the assumption that 

 this area was before recent uplift a vast plain rather than a moun- 

 tainous tract when arid cHmate was inaugurated. Inappreciable 

 aid from stream corrasion in this prodigious regional depletion is 

 indicated by the very fact of the prevalence of aridity itself. This 

 region is one of the best extant, demonstrating beyond peradven- 

 ture the almost boundless potency of the wind as an epicene power 

 in re-forming the face of earth. 



For general purposes of earth study no part of our land is so 

 favored as New Mexico. More diverse phenomena are crowded 

 together in limited space than perhaps anywhere else on our globe. 

 Every known category of geologic process appears to be repre- 

 sented. Every known cause of geographic product seems to have 

 been in operation. In great variety and with diagrammatic dis- 

 tinctness of textbook illustration are the larger rock structures 

 displayed. Everything, too, is on such a gigantic scale. Such 

 phenomena as dikes and faults have to be viewed from afar, from 

 distances of miles, in order to get proper perspective of their 

 relations. Orographic features, which are usually assumed to be 

 structural, are found to be mainly erosional. 



From the lofty cornice of the Sandias a landscape prospect 

 spreads out a distance equal to that from New York to Chicago. 

 Billows of mountain ridge take on an aspect of choppy sea as 

 viewed from the deck of an ocean hner. The silver thread of the 

 Rio Grande glints in the light of the desert sun for 400 miles until 

 finally lost on the verge of the world— so clear is the dry, thin air 

 of the desert. 



The crystalline framework of the region is both varied and 

 substantial. CrystaUine schists of the fundamental complex are 



