7IO MARIUS R. CAMPBELL 



5. Chemical solution. 



6. Wind action, 



7. Physical or chemical segregation. 



8. Glacial action. 



9. Uprooted trees. 



10. Spring and gas vents, 



11. Fish nests. 



From the widespread distribution of the mounds it is evident 

 that, if they have a common mode of origin, this mode of origin must 

 be such that it will fit a variety of climatic, geologic, and topographic 

 conditions. On this basis it is easy to rule out as general causes 

 a number of the above hypotheses without discussing them in detail. 

 For instance, on the sea terrace back of San Diego, Cal., where 

 the mounds are beautifully developed, or on the prairies south of 

 Tacoma, Wash., the hypothesis which attributes their origin to 

 fish nests might be applicable, for those localities have in recent 

 geologic time been under water; but certainly it would not be appli- 

 cable to the mounds which occur in other parts of the country. The 

 spring and gas-vent hypothesis might fit the conditions prevailing 

 in Louisiana or Texas, but mounds are just as abundant in areas 

 in which neither of these agencies has acted. It is evident, there- 

 fore, that this hypothesis cannot have a broad application, and 

 consequently may be eliminated. The mounds resulting from 

 uprooted trees have been cited as analogous to the mound in question, 

 but such a hypothesis would never have been advocated by a person 

 thoroughly famihar with the mounds in their best development. 

 We should be obliged to presuppose the existence of giant sequoias 

 over the low arid region of southern CaHfornia and Arizona, and 

 over the moist humid prairie of Texas and Louisiana. Manifestly 

 this is absurd and may be disregarded. Glacial action might be 

 appealed to in explanation of the mounds of Washington, but evi- 

 dently is not applicable to the great number of mounds found in 

 southern California and the Mississippi valley. 



By this method of elimination the number of hypotheses has been 

 reduced to seven, but these seven have a far greater degree of proba- 

 bility, and hence will have to be considered in detail before they are 

 discarded. 



