Grüger, Eberhard (1972): Age model of the Pittsburg Basin core. PANGAEA, https://doi.org/10.1594/PANGAEA.707457, In: Grüger, E (1972): Pollen and macrofossils profiles and age determination from the Pittsburg Basin in the lowlands of south-central Illinois. PANGAEA, https://doi.org/10.1594/PANGAEA.714979