1.1 Location Map of circular features

2.1 Geologic column for southeastern Missouri

2.2 Age relations of crystalline rocks

2.3 Showing location of study area with respect to regional structural features

3.1 Sites of Precambrian samples taken from drill cores

4.1 Circular features on MSS image

4.2 Top of the Precambrian

4.3 Top of the Upper Cambrian

4.4 Geologic Map

4.5 Map of faults and sinkholes

4.6 Bouguer gravity map

4.7 Aeromagnetic map