. Geology and underground water resources of northern Louisiana . 130. *^ McGee, W. J., The Lafayette formation; Twelfth Ann. Rept. U. Survey, pt. i, iSgr, pp. 347-521. 291 44 Geol. Surv. La. Report op 1905 [,. 4 waters used in the irrigation of that region. North of the Cat-ahoula sandstone their occurrence is essentially fragmentary, andthey appear and disappear in an extremely irregular shown by wells, they are commonly thickest in the largevalleys, where they have been concentrated by erosion subsequentto their original deposition, but they do not normally outcrop on
. Geology and underground water resources of northern Louisiana . 130. *^ McGee, W. J., The Lafayette formation; Twelfth Ann. Rept. U. Survey, pt. i, iSgr, pp. 347-521. 291 44 Geol. Surv. La. Report op 1905 [,. 4 waters used in the irrigation of that region. North of the Cat-ahoula sandstone their occurrence is essentially fragmentary, andthey appear and disappear in an extremely irregular shown by wells, they are commonly thickest in the largevalleys, where they have been concentrated by erosion subsequentto their original deposition, but they do not normally outcrop onthe surface of the present river flood plains and on the adjoiningterraces, though they are frequently exposed in the base of theriver banks at low water and are generally abundant where theterraces grade into the adjacent hills. They are notably absent in regions of very calcareousclays, as in the Jackson area in Louisiana and the regionsunderlain by the more calcareous beds of the Cretaceous, ^^apeculiarity of distribution due to two factors: (i) The cla3^ey. ^oj-v-jiu(. SyijT-cJaj)^^^:—^^TT .—-_- L SdncJyC^y^ Fig. 20.—North-south section showing Lafayette and younger gravels passing beneaththe clays of the Port Hudson and supplying artesian wells in southern Louisiana. layers of a gently sloping unconsolidated Coastal Plain series aregenerally more easily eroded than the sandy beds, and the sur-ficial beds are therefore really more completely removed along theoutcrops of the clay layers; (2) it is not always possible to statepositively that these Lafayette and younger beds are absent fromthe weathered outcrops of the sandy layers of the older CoastalPlain series, and it often happens, because of the absence ofpronounced lithologic differences, that the Lafayette beds are Also observed in Mississippi and Alabama (Geology of the Coastal Plainof Alabama, Geol. Survey Alabama, 1894, p. 63; Agriculture and Geology ofMississippi, i860, p. 5; Geol. Survey Louisiana, Rept, for
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