NATURAL MOUNDS 711 



The hypothesis of physical or chemical segregation was proposed 

 by Branner/ but absolutely no evidence was advanced in support 

 of it. He says: 



One other theory has been in my own mind for several years, but it is almost 

 entirely without observations to support it, and it is perhaps too vague to be 

 clearly expressed. The idea is that in solutions of certain kinds, long exposed 

 to weathering agencies, chemical reactions possibly take place around centers 

 that result in the transfer of minerals in solution, and the precipitation in nuclei 

 that are now represented by the position of the mounds, while the withdrawal 

 of these minerals from the intervening areas causes the depression around the 

 mounds. 



Purdue^ found himself at a loss to account for similar mounds 

 in the Arkansas valley, and took refuge behind Branner's vague 

 hypothesis, but he likewise failed to produce any direct evidence to 

 substantiate it. Manifestly in the present stage of our knowledge 

 this hypothesis has no support, and, until such evidence is presented, 

 it need not be considered. 



The question of wind action is not so easily disposed of; doubtless 

 many mounds have been produced by such action, and probably 

 many others of an entirely different origin have been modified by 

 the action of the wind. Nevertheless the great number of natural 

 mounds are far too symmetrical in profile and in plan to have been 

 formed by wind-blown material. Usually it is supposed that dunes 

 may be recognized by their unsymmetrical shape, while the mounds 

 are noted for their symmetry; consequently the only resort was to 

 suppose that they are the result of wind acting in various directions. 

 It is possible to conceive that fine, dry material may be heaped up 

 by winds blowing first from one direction and then from another, 

 producing a measure of symmetry; but when one considers the vast 

 territory over which these mounds occur both in dry and in humid 

 climates, it is evident that such special conditions could not have 

 prevailed, and thus we are forced to drop this hypothesis. 



We are thus reduced to five hypotheses, but, since No. 2 and No. 3 

 are essentially the same as far as the mode of origin is concerned, 



1 J. C. Branner, "Natural Mounds or ' Hogwallows, " ' Science, N. S. Vol. XXI, 

 No. 535 (March 31, 1905), pp. 514-16. 



2 A. N. Purdue, "Concerning the Natural Mounds," Science, N. S., Vol. XXI, 

 No. 543 (May 26, 1906), pp. 823, 824. 



