GEOLOGY 147 



climatic changes nearer to the present and read their re- 

 action on life within the history of man. This seems en- 

 tirely unwarranted because of the fact that rainfall once and 

 always means erosion, the sacrifice of straight lines and 

 sharp angles, for gradation and curves. A glance only at 

 the present landscape disproves this at once as curves are 

 not characteristic of New Mexican topographic architecture. 

 If abundant rainfall was characteristic of the past such as is 

 claimed by some authorities as necessary to support a much 

 larger population than is found here at present, the indica- 

 tions of such humidity would be evidenced in a corrugated 

 topography, and the intermittent streams of the common 

 arroyos would long age have turned the average evenness of 

 all topography not mountainous into general roughness and 

 bad-lands. Scattered about over the whole state are ruins of 

 once populous aboriginal towns. These ruins built of stone, 

 cemented together, not with mortar, but with adobe, could 

 not withstand the humidity of a very damp climate. The 

 conclusion which must inevitably be reached by those who 

 travel over wide areas of the state and see it more as a whole 

 than a part, is, that what is now the order of affairs as far as 

 climate is concerned, has, at least in the history of man, al- 

 ways been thus. The most inharmonious characteristics of 

 all the major topographic features of the state, are the broad, 

 well eroded valleys, such as the Puerco, Rio Grande and Pe- 

 cos, with adjustment and age carried on so far as to parcti- 

 cally eliminate all falls or rapids, and the intervening divides 

 scarcely attacked at all by tributaries. Since precipitation 

 makes river systems, or, in other words, developes a well 

 worked out drainage by many tributaries to the main stream, 

 we must necessarily conclude that this has not been the case 

 and that glaciation at the head waters and occasional floods, 

 are, on the whole responsible for the major phenomena occu- 

 pying the present drainage system. 



HUMIDITY AND CLIMATE 



New Mexico has a variety of climates. Due to the eleva- 

 tion of the northern part of the state, considerable snow and 

 cold weather are characteristic of the winter season, while 

 moderate temperatures and sufficient rainfall are character- 

 istic of the summer months. Throughout the central part of 



