Shatter cones in Illinois: Evidence for metoeritic impacts at Glasford and Des Plaines

Shatter cone fragments were recovered from rock cores at two previously suspected, but heretofore unverified, impact structures in Illinois. Both sites are buried features known from geophysical surveys and drill holes. Shatter cones are accepted widely as field criteria of meteoritic impact. Detection of these shock indicators in both the Glasford Structure and the Des Plains Disturbance upgrades these sites in Earth's inventory of known and suspected impact structures from possible impact sites with compatible structure and morphology to probable impact structures which possess also evidence of shock metamorphism.