| Paleozoic Stratigraphy of the Upper Midwest, USA |
|---|
| Dates approximate |
| Maquoketa Group (446–440 Ma) |
| Galena Group (454–446 Ma) |
|
| Platteville Limestone (455–454 Ma) |
| Glenwood Shale (~455 Ma) |
| St. Peter Sandstone (~459–~455 Ma) |
| Knox Unconformity (~470-~459 Ma) |
| Knox Supergroup (~497-~470 Ma) |