File:Map showing the distribution of the better known parts of the Pliocenesystem – Geology (1907) (14753463126).jpg

Identifier: geology00cham (find matches)
Title: Geology
Year: 1907 (1900s)
Authors: Chamberlin, Thomas C. (Thomas Chrowder), 1843-1928 Salisbury, Rollin D., 1859- joint author
Subjects: Geology
Publisher: New York, H. Holt and co.
Contributing Library: Internet Archive
Digitizing Sponsor: Internet Archive

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tile deposits. Ofthe major examples of Pliocene deposits of this class, those formedin the intermontane basins, abundantly exemplified in the Great basin,are the most obvious and unquestioned, though largely misinterpretedas lacustrine deposits. Lacustrine deposits are, however, presentand extensive in this region. 1 In its broadest sense, all sedimentary formations on land or tinder water areaggradational, but deposits under seas and lakes have their own distinctive terms,marine and lacustrine, and deposits made in the channels or on the flood plains ofrivers have their designations, fluvial or fluviatile, and alluvial. The term aggra-dation is coming into use to designate a group of complex deposits that take placeon land partly by overburdened rivers, but quite largely by temporary streamlets,slope-wash, sheet-wash, and miscellaneous agencies that remove material fromuplands and deposit it on flat lands, and it is in this sense that it is employed here, 296 THE PLIOCENE PERIOD. 297
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Fig. 459.—Map showing the distribution of the better known parts of the Pliocenesystem. The conventions are as in other maps, except that the area of the Lafay-ette, along the Atlantic and Gulf coasts, is marked by vertical dashes. This for-mation is doubtless more wide-spread than the map shows, as indicated in thetext. Relatively little of the exposed Pliocene is marine. 298 QEOIOQY. Over areas much greater than those occupied by lakes in Pliocenetimes, and over tracts which never formed parts of definite Hood plains,broad aprons l detritus brought from the higher slopes are accumu-lating now, and similar accumulations were quite surely making inPliocene times. Such accumulations are most considerable on theflanks of mountain ranges where precipitous slopes join plains oflow gradient. Particularly is this the case where the climate is sub-arid, and the rain falls in sudden and copious showers, largelyconcentrated on the mountain heights, while the thirsty plains below,cove

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