Answer:
The downfold or trough of a fold is called a syncline.
Step-by-step explanation:
Anticline: An anticline is a geological fold or structure in which rock layers have been bent or folded so that the oldest rock layers are at the core or center of the fold, and the youngest layers are on the outer edges. An anticline typically forms an arch-like shape, with the rock layers curving upwards from the center. It is characterized by the convex (upward) curvature of the rock layers.
Think of an anticline as an "A" shape, where the "A" stands for "arched."
Syncline: A syncline, on the other hand, is also a geological fold or structure, but it's the opposite of an anticline. In a syncline, the rock layers have been bent or folded so that the youngest rock layers are at the core or center of the fold, and the oldest layers are on the outer edges. A syncline typically forms a U or trough-like shape, with the rock layers curving downwards from the center. It is characterized by the concave (downward) curvature of the rock layers.
Think of a syncline as a "U" shape, where the "U" represents the downward curve.
In summary, an anticline is an upward-arching fold where the oldest rocks are in the center, while a syncline is a downward-arching fold where the youngest rocks are in the center. These geological structures are important for understanding the history and composition of rock layers in the Earth's crust and can have significant implications for various geological processes