. Bulletin of the Geological Society of America. Geology. 790 J. BAKRELL xMEASTTREMENTS OF GEOLOGIC TIME and wave action to fluctuate in level; the extreme conditions of excep- tional years are especially potent in upbuilding or in down-scour. Slow changes in sealevel, hundreds or, more usually, thousands of years in length, form pulsations of a higher order which affect marine and delta deposits. Climatic fluctu^ations of short and long periods cause varia- tions in the supply of sediment and the carrying power of rivers. These oscillatory rhythms are combined witli the discontinuous movement
. Bulletin of the Geological Society of America. Geology. 790 J. BAKRELL xMEASTTREMENTS OF GEOLOGIC TIME and wave action to fluctuate in level; the extreme conditions of excep- tional years are especially potent in upbuilding or in down-scour. Slow changes in sealevel, hundreds or, more usually, thousands of years in length, form pulsations of a higher order which affect marine and delta deposits. Climatic fluctu^ations of short and long periods cause varia- tions in the supply of sediment and the carrying power of rivers. These oscillatory rhythms are combined witli the discontinuous movements of. Figure 4.—Diagram postulating a progressive Tilting of the Crust, comhiiied with a rhythmic Elevation and Depression of Baselevel This diagram illustrates a variable rate of sedimentation dependent on' baselevel and distance from axis of tilting. R = radius of oscillation. 0, 1, 2, 3, etcetera, represent the position of baselevel at equal time intervals. tilting which are not oscillatory, but irregular and progressive in one direction. In studying the stratigraphic consequences of the combination of the two, the tilting may be regarded as progressive—that is, as con- tinuing longer than the other rhythms—and the latter as producing a parallel rising and falling of the baselevel. In such rise and fall tbe motion at the turning points is for most kinds of motions very slow, as in the tidal ebb and flo\A', or may be even arrested until sufficient force has become accumidated. This combination of progressive tilting witli. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Geological Society of America. [New York : The Society]
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