Geology . Fig. 446.—Columnarsection showing thesuccession of for-mations in westernMontana. (Peale,U. S. Geol. Surv.) THE MIOCENE PERIOD. 269 small areas (lakes?) in southern and central Montana. Later thearea of deposition became more extensive, and sediments were spreadwidely over the area between South Dakota and Mexico. Thoughthe lacustrine and fluvial phases of the formation have not been com-pletely differentiated, it appears that the latter were probably moreextensive than the To the north, the Loup Fork beds (prob-ably the equivalents of the Arikaree and Gering of western Nebr
Geology . Fig. 446.—Columnarsection showing thesuccession of for-mations in westernMontana. (Peale,U. S. Geol. Surv.) THE MIOCENE PERIOD. 269 small areas (lakes?) in southern and central Montana. Later thearea of deposition became more extensive, and sediments were spreadwidely over the area between South Dakota and Mexico. Thoughthe lacustrine and fluvial phases of the formation have not been com-pletely differentiated, it appears that the latter were probably moreextensive than the To the north, the Loup Fork beds (prob-ably the equivalents of the Arikaree and Gering of western Nebraska 2)are often unconformable on the deformed and eroded White River. Fig. 4-17.—Court House and Jail Rocks. Buttes of the Arikaree (Miocene) for-mation of western Nebraska. (Darton, U. S. Geol. Surv.) beds, and like the latter have given rise to bad-land topography,to striking monuments, buttes, etc. (Figs. 447-449). The Santa Fe(fluvial) marls of Xew Mexico are correlated with the Loup In Texas, beds of terrestrial sediments are wide-spread inthe Llano Estacado region, and have been described under the namesLoup Fork and Goodnight, though the Goodnight beds are sometimesregarded as Terrestrial aggradation was doubtless in progress at many otherpoints in the west, though other considerable formations have notbeen recognized or not 1 See Haworth, Univ. Geol. Surv. of Vol. II, p. 2S1. 2 Darton, U. S. Geol. Surv., 19th Ann., Pt. IV, and Camp Clarke and Scotts Bluff,Neb. folios, U. S. Geol. Surv. 3 Johnson, I). W., Geology of the Cerillos Hills, X. M., Sch. of Minos Quarterly,Vol. XXIV, p. 313, 1903. Bibliogra
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