14 LIFE OF THE PLEISTOCENE 



or northeast, for the shells found by Drs. Bell and Ells are all of Arctic species. 

 If the shells be evidence of an incursion of the sea, their occurrence, so far as 

 known on this second, or Calumet beach only, would indicate this stage (or a 

 part of it) as the time of the incursion, and the southern range of all these 

 species at the present day would indicate that the incursion was not from the 

 northeast through the St. Lawrence embayment, but from the south, through a 

 Mississippi embayment. 



"In view of these apparently conflicting considerations, final judgment 

 concerning the interpretation of the shells must be suspended until further 

 evidence is forthcoming. " 



The finding of marine fossils in the fields near Chicago Lawn raised a serious 

 question as to their origin. The presence of certain Crustacea (My sis) in the 

 lake as well as of such plants as the beach pea (Lathyrus maritimus), the beach 

 plum (Primus maritima), and the seaside spurge (Etiphorbia poligonifolia) 

 has led several writers to the conclusion that the waters of Lake Michigan were 

 once salt. The presence of these plants and crustaceans are, however, not 

 sufficient evidence on which to build a theory of this kind. At first it might be 

 thot that the fossil shells found on Mr. Welch's farm offer indubitable evidence 

 of the presence of marine waters at this stage of postglacial history There 

 are, however, several physical factors to be taken into account. The species 

 recorded are all of southern distribution, living plentifully in the Gulf of Mexico 

 or the waters of the Atlantic Ocean bordering the southern and southeastern 

 coast of the United States. Therefore, the incursion of the sea must have been 

 from the south by way of the Mississippi Valley and not from the northeast 

 by way of the St. Lawrence Valley. 21 If there was such an incursion, there 

 should certainly be evidences in the territory lying to the south of the area in 



21 The species found on Mr. Welch's farm are noted below. A list of a few species from 

 the Montreal marine deposits is also given, in a parallel column; the difference in the two 

 faunas is at once manifest. 



Chicago Montreal 



Mollusks Mollusks 



Ostrea virginica Saxicava arctica 



Area transversa Mya arenaria 



Venus cancellatus Mya truncata 



Venus mercenaria? Macoma balthica grosnlandica 



Pecten sp. (Chlamys irradians?) Cardium grcenlandicum 



Gnathodon cuneatus Mytilus cdulis 



Fulgtir perdersus Chlamys islandicus 



Cerithium species (apical whorls) Acmcea cocca 



Ceritkiopsis species " Littorina palliata 



Coral Scala grosnlandica 



Oculina robusta Lunatia heros 



Trichotropis borealis 

 Buccinum undatum 



