SNAILS AND THE SOIL — VAN CLEAVE 281 



portion of the soil, because of difference in its consistency. In such 

 an old lake bed, the action of a meandering stream cutting its ever 

 widening and wandering channel might readily leave isolated patches 

 of shelly material on slightly elevated places where at an earlier date 

 the shell material had been a continuous sheet in the deepest part of a 

 former pond or lake. 



SUMMARY 



By the way of summary, it may be stated that all the accumulations 

 of shells, whether from present day or ancient origin, represent stored 

 supplies of lime, available for modifying the soil and making it suit- 

 able for plant growth. At times, the shell deposits of cultivated land 

 occur in combination with conditions unfavorable to crop growth. In 

 these instances the shells are only indicators of other conditions which, 

 in turn, are responsible for adverse conditions because when adequate 

 drainage or manuring is carried out the faults are corrected. Often 

 the shells of snails are found on agricultural lands, as is the case of 

 marl and loess deposits, and apparently they add to the productiveness 

 of the land. The observable snail shells in the soil do not comprise the 

 entire effect of snails upon the soil. In many instances the shells are 

 finely broken and unrecognizable and, in the loess, ground water is 

 known to dissolve out lime and to translocate it to lower soil levels or 

 to the ground water where it becomes a part of the lime supply of 

 natural waters. Furthermore, the snail shells of long-past ages are 

 united with other limy shells of animals in the formation of the lime- 

 stone deposits which are then secondarily used for agricultural pur- 

 poses. In this discussion no attempt has been made to evaluate the 

 place of living snails in the production of humus and in the addition 

 of organic matter to the soil. 



REFERENCES CITED 



Eakeb, Fkank C. 



1921. The importance of ecology in the interpretation of fossil faunas. 

 Ecology, vol. 2, pp. 277-280. 



1930a. The molluscan fanua of the southern part of Lake Michigan and its 

 relationship to the old glacial Lake Chicago. Trans. Illinois Acad. 

 Sci., vol. 22, pp. 186-194. 



1930b. Influence of the glacial period in changing the character of the mol- 

 luscan fauna of North America. Ecology, vol. 11, pp. 469-480. 



1936. Remains of animal life from the Kingston kitchen midden site near 



Peoria, 111. Trans. Illinois Acad. Sci., vol. 29, pp. 243-246. 



1937. Pleistocene land and fresh-water Mollusca as indicators of time and 



ecological conditions. In symposium on "Early Man," pp. 67-74. 

 Lippincott. 

 1939. Fieldbook of Illinois land snails. Illinois State Nat. Hist. Surv., 

 Manual 2, pp. 1-166. 



