like ash falls, resemble sedimentary rocks because they are laid down horizontally as well.
Figure 7.4: The layered rocks of the Grand Canyon from the rim. ( 38 )It’s important to remember that sediments are deposited horizontally when thinking about
geologic structures. This is because you can trace the deformation the rock has experienced
by seeing how it differs from its original horizontal, oldest-on-bottom, position (Figure7.5).
Geologic structures are the folds, joints and faults that are caused by stresses.
Folds
When rocks experiencing compressive stress deform plastically, the rocks crumple intofolds.
Folds are just bends in the rock. You can easily make folds by placing your hands on opposite
edges of a piece of cloth and pushing the cloth together. In layered sedimentary rocks, you
can trace the folding of the layers with your eyes (Figure7.6).