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syncline
syncline n. 
/ˈsɪŋklaɪn/ a synclinal fold or depression; (see also quot. 1972); cf. synform n. at syn- prefix 1.
/ˈsɪŋklaɪn/ a synclinal fold or depression; (see also quot. 1972); cf. synform n. at syn- prefix 1.ΘΚΠ
the world > the earth > structure of the earth > structural features > fold or dip > [noun] > syncline
synclinal1855
syncline1874
downwarp1903
1874 J. Geikie Great Ice Age xxi. 288 (caption) Diagrammatic view of synclines and anticlines.
1893 B. Willis in 13th Ann. Rep. U.S. Geol. Surv. 1891–2: Pt. 2 219 The two great types of folds are the syncline and the anticline. The syncline..is a depression of the strata from a flat to a basin-shaped form.
1937 Trans. Royal Soc. Edinb. 59 81 In common tectonic practice, an anticline has come to be understood as a fold with a core of previously underlying rocks, and a syncline as a fold with a core of previously overlying rocks.
1972 Gloss. Geol. (Amer. Geol. Inst.) 718/2 Syncline, a fold, the core of which contains the stratigraphically younger rocks; it is concave upward.
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