IOWA ACADEMY OP SCIENCE 
141 
McGee® has shown the general plains-surface of northwestern Mexico to be 
worn out on the bevelled edges of strata composing the substructure, although 
he ascribed the planation to sheet-flood eros:i)n. In South Africa Passarge® 
has r^ognized the whole of the elevated interior tableland as a surface of the 
same kind. Davis'^ has appeared lately to be inclined to believe that some of 
the high plateaus of central Asia belong to this same class rather than to that 
i)f normal peneplanation. 
In the arid region many of the principal planation phenomena which are 
displayed and which are attributed to normal hydric erosion should be doubtless 
referred to other geologic agencies. Of all th^e eolian influences appear to be 
far most effective. 
5. Bull. Geol, Soc. America, Vol. VIII, pp. 87-112, 1897. 
6. Naturw. Wochensch. , N. S. , III Bd. , pp. 657-665, 1904 
7. Journal of Geology, Vol. XIII, p. 405, 1905. 
