278 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



directed to the the fact that deposits of shells are found in environ- 

 ments different from those in which they originated. There are many 

 factors responsible for this fact, but the chief of them may be grouped 

 under two headings: (1) translocation of the dead shells and (2) 

 physiographical changes of the earth's surface. 



TRANSLOCATION 



Water, wind, ice, and human agency are the chief factors in trans- 

 location and accumulation of dead shells in areas other than those in 

 which they originated on the bodies of living snails. Both recent and 

 remote geological times have contributed to the stock of shells now 

 found in the soil and, through the agencies for translocation, shells 

 from past ages may become elements in the construction of soils at the 

 present time where they may be mixed indiscriminately with shells 

 recently produced. 



Water. — Many limestone deposits include fossil shells of snails and 

 clams of long-past geological ages along with the remains of multi- 

 tudes of other organisms having limy skeletons, such as the corals, 

 certain types of Protozoa, and echinoderms. These components of 

 the sedimentary limestones provide deposits of lime utilized by modern 

 mollusks in the production of their shells. These same limestone de- 

 posits are utilized commercially in the production of limestone for 

 agricultural purposes. Here the shells of snails, clams, protozoans, 

 and corals of geologically ancient oceans provide a renewed source of 

 lime on lands where weathering, leaching, and cropping have depleted 

 the natural supplies. Much of the lime now available in fresh water 

 thus comes from the geologically old lime deposits, largely of marine 

 origin. Ground water, flowing over and through the limestone, dis- 

 solves the lime and makes it available for the aquatic animals in fresh 

 water. 



Another type of translocation by water is that in which running 

 water carries dead shells and lays them down in a new location either 

 at the bottom of a lake or pond or along the margins of streams. If 

 the water carries much abrasive material the shells may be ground 

 fine and mixed with the mud and sediment, though often they are un- 

 injured. When the course of the stream is changed, through natural 

 or human agency, or when the bed of a lake or swamp is drained, the 

 accumulated shells are exposed as marl deposits and attract more at- 

 tention than they could while covered with water. 



Surface waters on rolling lands often tend to wash dead land shells 

 into gullies or against obstacles such as the stems and roots of grasses 

 where definite windrows accumulate awaiting decomposition or 

 further translocation by other agencies. In fact, an examination of 

 gullies and hillsides often reveals to the collector dead shells which 



