A succession of molluscan faunas preserved in the upper 366 cm of a vibracore recovered from the Cowles Bog area records a series of long- and short-term environmental changes in the Lake Michigan basin since the low-water Lake Chippewa phase.

The rise in the water to the Nipissing I level during the post-Lake Chippewa transgression affected the water table landward from the lake and brought into existence a small lake or pond at the core site. This event is recorded in the core at a depth of about 366 cm by a change in lithology from interbedded organic layers and...