followed by a shallow deposit of glacial till during the Wisconsin Glacial Period. The quarry operations have extracted the upper Ordovician carbonates of the Platteville and Galena (Prairie due Chien) groups along the northern edge since 1906. Structure The Structure is a deeply eroded complex crater. Since the original impact, the structure has eroded over , eliminating the crater and other surface elements. Ring anticline The ring surrounds the impact site, separating it from the surrounding flat-lying regional bedrock. The ring is about in radius around the central disconformity. Ring depression The ring depression is the result of the displacement of materials at lower levels to fill the void created as the central uplift rose. Studies at other sites similar to the Kentland structure have found the depression to be the equivalent of the material that would have moved under the uplift as it occurred. Central Uplift A cross section of the uplift, beginning on the outer edge, moving towards the middle, is shown in the image above. See also List of impact craters on Earth References Additional sources Cohen, A.J., Bunch, T.E., and Reid, 1961, Coesite discoveries establish cryptovolcanics as fossil meteorite craters: Science, v.134, p. 1624-1625. Collet, J., 1883, Geological survey of Newton County: Ind. Dept Geol. and Nat. Hist., 12th Ann. Report, p. 58-59. Dietz, R.S., 1947, Meteorite impact suggested by orientation of shatter cones at the Kentland, Indiana, disturbance: Science, v.105, n.2714, p. 42-43. Dietz, R.S., 1960, Meteorite impact suggested by shatter cones in rock: Science, v.131, n.3416, p. 1781-1784. Dietz, R.S., 1963, Cryptoexplosion structures-a discussion: Am. Jour. Sci., v.261, p. 650-664. Dietz, Robert S.; Shatter Cones in Cryptoexplosion Structures (Meteorite Impact?); The Journal of Geology; Vol. 67, No. 5 (Sep., 1959), pp. 496–505 Gutschick, R. C., Geology of the Kentland dome structurally complex anomaly, northwestern Indiana (Field Trip 5). Field trip in Midwestern Geology, Annual Meeting, Geological Society of America, Indianapolis, v. 1, pp. 105–138. 1983. Gutschick, R. C., Geology of the Kentland structural anomaly, northwestern Indiana—update. Purdue University, Department of Geosciences, and Geological Society of America, North-central Section, Guidebook 4, 38 p. 1982. Gutschick, R.C., 1976, Geology of the Kentland structural anomaly, northwestern Indiana: Guidebook for 1976, North-Central GSA Meeting, 59 p. Gutschick, R. C., Geology of the Kentland impact structural anomaly. Meteoritical Society, 35th Annual Meeting, Guidebook for Field Trip. 1972. Gutschick, R. C., Geology of the Kentland impact structural anomaly, northwestern Indiana.