WIXD-GRATED MESAS 



2 33 



the coulees from the Tintero, on the Mesa Eedonda, west of the San 

 Mateo, that finally enter the channel of the Eio San Jose at a level 

 considerably below that of the great flow already mentioned. 



Four distinct and notable periods of volcanic extravasation are thus 

 recorded, between the first and last flows of which more than 1,000 feet 

 of rock were removed from the entire region about. There are in the 

 district many other lava-flows at other elevations; but between the four 

 especially mentioned definite time-relations are readily established. 



At the present time particular interest attaches to the mesas and 

 their origin. Normal water-corrasion manifestly did not accomplish 



Fig. 5. A Lofty Isolated Mesa neab Acoma Pueblo; capped by Lav(\ and a Hard 



Sandstone Stratum. 



the strange sculpturing of the country. In these relief features we 

 seem to be introduced to an erosive force as potent as water but which 

 we are just beginning fully to appreciate. Mesas appear to furnish the 

 most direct and convincing testimony we have of the tremendous power 

 of the wind in affecting general erosion under conditions of aridity. 



That water could not possibly produce such effects is shown in a 

 number of ways. On the continental divide the streams are their 

 smallest. On a vast plain so situated drainage features are necessarily 

 insignificant. Eainfall is the scantiest. These three conditions com- 

 bined with arid climate give water-action small opportunity to vigor- 

 ously erode. On every hand the country clearly shows it. It is equally 



