134 LIFE OF THE PLEISTOCENE 



VI Peat and drift wood 10 " 



V Lake silt (no shells) 8 " 



IV Semi-ligneous peat 12 " 



III Shells and lake drift 8 " 



II Blue clay 7 " 



I Quicksand 7 to 10 feet 



The thickness of the sedimentary deposits above the sand is 81 inches or 

 6 feet 9 inches. The quicksand (stratum I), perhaps, represents the period 

 of Lake Dowagiac when the glacial waters drained into the Kankakee River, 

 loaded with sediment (Plate XLVII, Fig. 1). The clay (stratum II) may repre- 

 sent a quieter stage, after the main drainage had shifted to the Chicago outlet 

 (Plate XLVII Fig. 2). Stratum III probably represents the bottom of a larger 

 St. Joseph River, for the species of naiads in this deposit are mostly of the river 

 type. An arm of Lake Chicago extended up the St. Joseph River from Benton 

 Harbor to about the vicinity of Berrien Springs 54 and the river drained into this 

 extension of Lake Chicago. 



The fluviatile mollusks could have reached this locality from two sources: 

 (1), by way of the Chicago outlet, across Lake Chicago and up the St. Joseph 

 River; and (2), by way of the Kankakee River when it was connected with 

 the St. Joseph and Dowagiac rivers at South Bend. The mussels are mostly of 

 the river type and their natural migration route would be by way of a river. 

 Just how long after the formation of Lake Chicago the St. Joseph-Kankakee 

 drainage persisted is not definitely known, but it is believed to have continued 

 for some time in a more or less modified form. The naiades represent a climate 

 fully as warm as the present and they probably would not invade the waterways 

 of an icy drainage. Certain boreal types of mollusks could and evidently did 

 take advantage of this waterway at an early stage. It is possible that both 

 drainages were used and the fauna may represent a mixture of the two migra- 

 tions. This stratum would seem to correlate with the Toleston stage of Lake 

 Chicago and may include, also, some deposits made during the Calumet Stage. 



The five and a half feet of silt and peat above the shell deposit represent 

 the later stages of this locality and indicate its change from a river to a lake 

 and finally to its present marsh-bog character. Stratum IV indicates a period 

 of low water between higher water — lake or river — conditions. The Mollusks 

 (42 species) and other remains of life in the shell deposit are listed below: 55 



Lasmigona compressa (= pressus) Plenrocera elevatum 



" costata {^rugosa) Goniobasis livescens 



Anodonta grandis footiana Valvata tricarinata 



Anodonioides subcylindraceus Amnicola limosa 

 Alasmidonta cakeola (=deltoidea) " lustrica 



" See Leverett, Illinois Glacial Lobe, plate XV. 

 "Walker, Nautilus, XI, p. 121; XIII, pp. 34, 55. 





