22 



SMITHSONIAN INSTITUTION 



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•iiiifiniiiitriiiii iiiiiitiTfim'- T-nr if 



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Fig. 21. — Typical valley and iiiuuntain range of the Plateau region of 

 Mexico. Yuccas and creosote bush on the hill-slope. (Photograph by 

 Foshag.) 



Fig. 22. — The "Bufa" of Mapimi. A typical mountain range of central 

 Mexico. Cretaceous limestone sloping gently to the soutli. (Photograph 

 by Foshag.) 



