280 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



sites. It is generally known that well-established trade routes had 

 been originated by the early American Indians and it is known that 

 they traded in and cherished some of the seashells, even though they 

 had to be transported long distances to the interior of the country. 



Modern man has also had his influence upon direct distribution of 

 shells. Through the oyster and other shellfish industries, including 

 pearl-button factories, huge spoil heaps of shells are accumulated in- 

 cident to commercial operation. In many instances, these wastes are 

 converted into commercial products for feeding poultry and as crushed 

 shell for lawns and gardens. 



PHYSIOGRAPHICAL CHANGES 



Elevations of the shoreline or depression of the water level of the 

 ocean, and even of lakes and rivers, often leave natural deposits of 

 dead shells exposed to the action of the weather and available for 

 building soil. Also, in the instances of the earth's crustal movements, 

 regions that were formed as rock deposits in the bottom of the ocean 

 become elevated and folded as hills and mountains, and deposits of 

 rocks containing snails and other lime-bearing shells become exposed 

 through weathering and folding of the strata. 



At times, outcrops of shells occur in isolated spots in fields. Physio- 

 graphical changes are likewise responsible for this phenomenon. 

 When these deposits occur in depressions, they are readily explainable 

 as due to the irregular shape of the lake or swamp on whose bottom 

 they were deposited or were brought in by various of the agencies men- 

 tioned above. However, in some instances the isolated patches tend 

 to be on slightly elevated ground, not in gullies. In such cases, only 

 speculation can be brought in as an attempt at explanation. The 

 writer believes that the most logical explanation is one that involves 

 considerable periods of time. At some past age, an old lake bed filled 

 up and in its bottom were deposited layers of shells overlain with other 

 deposits of sand or of muck. By changes in the drainage, streams 

 could cut through this level plain, sinking their channels through the 

 overlying deposits and finally through the shell accumulations. The 

 nature of the shell deposits left exposed by these newly established 

 streams would depend upon how long the streams had been flowing. 

 If the young streams had cut relatively straight courses, then the shells 

 would be exposed along the banks of the streams or long gullies when 

 the stream finally disappeared. Under other conditions, if the streams 

 were to continue for a long time, they would meander through the old 

 exposed lake bed cutting down and carrying away almost all of the 

 original shell deposit, leaving it only on knollsides and on slight eleva- 

 tions where the stream was unable to erode away the knoll, or other 



