A downward fold in rock layers where the youngest rocks are in the center and older rocks are on the outside, forming a trough-like structure. These folds form when rock layers are compressed and buckle downward.
From Greek 'syn' (together) and 'klinein' (to lean), meaning 'leaning together.' Coined alongside 'anticline' in the 19th century as part of the systematic geological vocabulary for describing folded rock structures.
The Appalachian Valley and Ridge Province is a spectacular example of alternating synclines and anticlines - from an airplane, you can see the zigzag pattern of ridges and valleys that follow these ancient folds! Synclines often become valleys because the younger rocks in their centers are typically softer and erode more easily.
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