AWvlpiiKKUHWlClKWi lUjKlWpWW 1 'I^Wi 



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Figure 2. Diagram illustrating terrace deposits on Rock River. 



A. Ground plan of river; a-b, points between which section was taken; c, point near 

 which section was taken; d, sand bar on which fossil shells are deposited after being dug from 

 bank by river. 



B. Section of terrace at c in A. a, fine rich black alluvium, 3 feet thick, containing shells 

 of Polygyra (Mesodon), Succinea, Lymnaea, Physa, etc., almost exclusively Pulmonata; b, 

 mixture of top and under stratum, 2 feet thick, containing also a mixture of both kinds of 

 mollusks; c, pure sand and fine gravel, 4 feet thick, containing great numbers of fresh water 

 Mollusca, as Unio, Sphaerium, Pisidinm, Campeloma, Pleurocera, Amnicola, Pyrgulopsis, 

 Somatogyrus, etc.; d, loose sand; e, Rock River (Copied from Shimek, Bull. Lab. Nat. Hist, 

 State Univ. Iowa, II, plate XIII). 



