410 ILLINOIS STATE ACADEMY OF SCIENCE 



about seven feet of marl and peat above the Niagara 

 limestone, both the marl and peat containing an abund- 

 ance of molluscan material. 



Collections made in three places below Chicago indi- 

 cate rather clearly that the Chicago biota migrated up 

 the Illinois and Desplaines rivers. A comparison of col- 

 lections made at Morris', Joliet, and Lemont' with those 

 of Lake Chicago indicate this migration route. 



The Joliet material contains more species because more 

 thoroughly collected. The other localities would doubt- 

 less yield additional species with more time for collect- 

 ing. The approximation of the Joliet species with those 

 found in Glacial Lake Chicago at Chicago strikingly in- 

 dicates that the Joliet fauna provided a reservoir from 

 which the Chicago region was populated. The Morris 

 material, though not large in number of species, contains 

 some critical species which also occur in the deposits 

 farther up the river. Additional collections from marl 

 and peat deposits in the Illinois and Desplaines valleys 

 will add more species records and strengthen the chain 

 of migration. The following table graphically shows 

 the relation of the Joliet species to the biota of the other 

 deposits along these rivers: 



Distribution of Aquatic Species in Different Localities 



1. Made bv Mr. H. E. Culver: see Journ. Geol., Vol. XXX, p. .58, 1922. 



2. Baker, Life of ^he Pleistocene, p. 56, 1920. 



