POST-GLACIAL MOLLUSCA FROM THE MARLS OF 
CENTRAL ILLINOIS* 
FRANK COLEINS BAKER 
Curator, Museum of Natural History, University of Illinois 
The study of the biota contained in marl beds, and in other 
deposits lying upon the till of the late Wisconsin ice sheet, has 
added greatly to our kriowledge of the post-glacial distribution of 
many mollusks and other animals, and has often provided data 
bearing on the changes of climate which have occurred during the 
interval between the retreat of the Wisconsin ice and the present 
time. The material that forms the basis for the present contribu- 
tion adds to our knowledge concerning the post-glacial distribution 
of a few lacustrine and fluviatile forms of mollusks. 
My thanks are due Dr. T. E. Savage, of the University of 
Illinois, for the opportunity of examining the material as well as 
for stratigraphic data bearing upon the deposit containing the 
collections; Dr. V. Sterki and Dr. Bryant Walker for the examina- 
tion of critical material; and Professor Frank Smith for assistance 
in collecting material from the vicinity of Mahomet. 
Marl deposits are extensively distributed in Michigan, Wis- 
consin, Maine, New Jersey, and other localities, being better known 
in the states named than elsewhere. Indiana, Ohio, and Illinois 
also contain marl beds of greater or less size, but these have not 
been as exhaustively studied for their biota. Marl deposits have 
rarely been reported from Illinois, a condition due to lack of 
observation rather than to absence from the territory. 
The study of these marl deposits is of great interest and some — 
value, a comparison of the marl fauna with the recent fauna usually 
showing a change from cold to temperate climate. Many species 
also indicate a more southward distribution during early post- 
glacial time. It is of importance that the marl deposits of the state 
< Contribution from the Museum of Natural History, University of Illinois, No. tr. 
659 
