NATURAL MOUNDS 709 



character of the local material. As the writer has observed them in 

 California and in Arkansas, they are made up of clay, or clay with a 

 slight admixture of gravel, depending upon the character of the under- 

 lying subsoil; but in Texas and Louisiana, according to report, 

 they are made up largely of sand, and in Missouri of chert fragments 

 from the Carboniferous limestones. 



So far as the writer has observed or has been able to obtain refer- 

 ences to them, mounds of a similar character occur in abundance 

 in Louisiana, Texas, Arkansas, Missouri, Kansas, Indian Territory, 

 Arizona, California, Oregon, Washington, Mexico, and Argentine 

 Republic.'^ Generally they are reported as occurring on low, flat 

 lands; but Turner^ has described and figured similar topographic 

 features covering low hills on the east side of the San Joaquin valley 

 in California, and recently Hill^ has noted their occurrence on the 

 high plateau of Mexico, nearly 7,000 feet above sea-level. 



To account for the origin of these mounds various hypotheses 

 have been advanced, but in most cases they are speculative only 

 and have little or no foundation in fact, or they are based upon 

 limited observations and fit only the conditions prevailing in one 

 locality. 



It is altogether probable that the mounds which have been noted 

 in various parts of the country are not exactly similar and have not 

 had a common origin, but this cannot be proven until they have 

 been more carefully studied, and studied by one person who can 

 compare the mounds in different localities and judge whether or not 

 they are all due to the same cause. 



The principal hypotheses may be summed up as follows: 



1. Human agency. 



2. Animal burrows, such as ground squirrels, gophers, and prairie 

 dogs. 



3. Ant hills. 



4. Water erosion. 



1 Since the above was written the writer has observed similar mounds on the 

 broad flat valley bottom near Logan, Utah. 



2 H. W. Turner, "Further Contributions to the Geology of the Sierra Nevada," 

 U. S. Geological Survey, Annual Report, Part i, pp. 681-83, Plate t,^. 



3 R. T. Hill, "On the Origin of the Small Mounds of the Lower Mississippi 

 Valley and Texas," Science, N. S., Vol. XXIII, No. 592 (May 4, 1906), pp. 704-6. 



