| Summary: | OROLOOr OP' THR HILL COUHTRY 9 Were this series of rocks all present in any given locality, and each itratum superimposed upon the other, the Fox Hills formation would come at the top of the series, and the Dakota sandstone at the bottom, as the oldest of all. It is the Dakota sand«tone in which the water is struck in boring artesian wells in some parts of this state, but generally in South Dakota. Naturally the question has arisen among the geologists, from whence came the materials with which the old Cretaceous sea in part became filled up ? This query can only be answered mainly by conjecture. There were probably Archaean and other lands of considerable extent east and west of the Cretaceous sea and thier drainage was largely into this sea. The age was tropical as to climate, there was more carbonic acid in the atmosphere than now, and likely a greater rainfall prevailed; under such conditions the elevated lands may be supposed to havj disintegrated more rapidly than such processes go on at, the present time, the torrents bearing the sediments resulting from rock decay seaward, in which they were spread by the waves and currents. Organic life contributed their remains to help form limestones on those parts of the changable sea-bottom productive of the right conditions. The shore-lines were probably never stationary through long periods, and the battering of waves against sea-cliffs causes them to break down, the fragments being reduced to pebbles, sand and an impalpable powder, which, settling in deep water, helps to form a clay bed. Lastly, the ancient sea may have had extensive islands, the wearing away of which assisted in the formation of the strata mentioned. As has been said, the sea-bottom covering the states that have been indicated, lay at varied depths, and when the whole age is considered, also varied in the same areas, as portions of it subsided or were raised by crustal or epigeronic movements ■ot directly connected with deposition of sediment. These variations together with the shifting of the coast lines, pro-, duced a corresponding variation in the character of the rocks, Scanned with a Zeutschel Zeta book scanner at 300 dpi. Edited in Multi-page TIFF Editor.
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