Decorah Shale - Green, calcareous shale; thin limestone interbeds. In a few places capped by thin (less than 20 feet) erosional remnants of limestone of overlying Galena Group (not shown on map). Largely restricted to south half of county. Unit crops out in bluffs of Mississippi River in South and West St. Paul. Formerly mined in South St. Paul above Pickerel Lake for clay to make brick and tile.
Platteville and Glenwood Formations - Fine-grained dolostone and limestone of Platteville underlain by thin, green, sandy shale (3-5.5 feet thick) of Glenwood. Extensive outcrops in bluffs along Mississippi River in St. Paul. Platteville formerly quarried for rock aggregate and building stone in bedrock terraces of South St. Paul.