ANTICLINE (Gk. anti, against, oppo site + K5ivem, klincin, to incline). In geology, a term applied to that form of rock-folding in which the opposite sides or limbs of the fold slope downward and away from the crest of the fold. Anticlinal axis is the axis or crest of such a fold. The anticline may he compared to the ordinary gable-roof—the axis corresponding to the ridge of the roof, while the limbs of the anti cline correspond to the slopes of the roof. When the anticlinal axis lies in a horizontal plane, which, however, is seldom the case, the layers composing the limbs of the fold are, after ero sion, exposed in parallel rows on either side of the axis; those layers of earlier age, and conse quently of lower stratigraphic position, occur)y ing positions nearer to the axis, and riff-versa. Thus, in an anticlinal ridge the crest of the ridge is occupied by rocks of a geologic age earlier than that of the rocks forming the flanks of the ridge. This condition is due largely to the fact that the rocks near the axis have suf fered greater compression and are consequently harder than are those of the flanks.
The supplementary condition to that of the anticline, or up-fold, is observed in the syncline, or down-fold, and indeed these two types of folds are usually found in close association; the feat tires of anticlines being. however, reversed in synclines. When anticlinal and synclinal axes are tilted and eroded, the component layers out crop in alternating convergent and divergent series to form zigzag ridges with intervening "canoe-valleys." a type of structure which is well developed in Pennsylvania. The term anti elinorium is applied to a compound anticline, and the term snneliaori111n to a compound syn cline. Anticlines are intimately associated with the occurrence of natural gas, it having been dem onstrated that the gas occurs at those portions of the gas-bearing stratum that have been thrust upward to form an anticlinal axis or dome. See DIASTROPHISM ; GEOLOGY: and for illustration, see plate accompanying the latter title.