| Summary: | 10 aeotoor omhe hill eouH.'HiY which had their origin in the old sea. Sandstones were of oft shore deposition and where a stratum of this rock occurs ofer a wide area, as in the case of the Dakota sandstone, it indicates, deposition by waves and currents in shallow waters, when the sea bottom was slowly sinking. The but little consolidated.' Fort Pierre formation is undoubtedly a deep water deposit, while limestone, largely composed of lime derived from shells, pulverized by the waves, with some admixture of clay and, »and, is also an off-shore deposit, but formed in deeper water, than sandstone. Shales are beds of clay, cemented or changed^ to the condition of soft, slaty rocks. Before leaving this brief survey of the old Cretaceous sea, a. few more explanations may be ventured. It will be borne in mind that it covered a very extensive portion of the continent, hence widely different conditions relative to depth, etc., may- and probably did prevail during the same epochs; a limestone., being in process of formation in one or more areas; clay in some others; and more rarely a sandstone m some other part, of the sea. A formation might cover an extensive area, but it could not be co-extensive with the whole. Nor were the different epochs wholly successive; thus, the deposition of the Font Pierre clay had probably not been completed when that, of the; Fox Hills sandstone was already begun elsewhere. The extinguishment of the ancient sea was not in the way of a sudden physical revolution, but occupied an enormous period of time. Between the Cretaceous and Tertiary ages there intervened a prolonged transitional stage called the Laramie Period. F'irst, allowing that at one time the Cretaceous sea had some connection with the Arctic Ocean,, it was cut off in that direction by an upraising of that part of the continent, and then or earlier that part of the sea that had covered Iovl* and Minnesota was pushed farther west by reascn of those regions becoming land areas. Next, what is now Texas and parts of adjoining states were raised above the ocean level nry$ Scanned with a Zeutschel Zeta book scanner at 300 dpi. Edited in Multi-page TIFF Editor.
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