The other is concave upward with younger rocks of Silurian shale and siltstone toward the center of curvature. The former is called anticline and the latter syncline. The sides of the folds are known as limbs,

• 而另一个褶曲向上凹，较新的志留系页岩和砂岩位于弯曲的中心部位，前者被称为背斜，后者则称之为向斜，褶皱核部两侧叫做褶皱的翼部。