Looking more closely we find that the strata in an anticline dip away from the axis, whereas the limbs of a syncline dip toward it. The ages of the rocks exposed in an anticline increase as we move towards the axis. In a syncline they decrease with the youngest in the middle. Since synclines and anticlines are usually paired, layers outcropping in plunging folds appear as zig-zag lines on the surface. The crests and troughs of the layers are aligned along the fold axis.
Crests point towards the direction of plunge for anticlines and away from it in synclines.
If rocks in the different layers have different rates of erosion, the result is a series of low-lying hills and valleys, such as seen in the Appalachian Valley and Ridge Belt. All rocks near the surface have fractures. Most are formed by uplift and cooling. We call these joints. Rocks on either side of a joint have not moved relative to one another.