The geologic force applied to rocks is called compression. Compression is the stress that squeezes rocks together. As a result of the compression rocks fold or fracture depending on their compressive strength or compression strength - the capacity of a material or structure to withstand loads tending to reduce size.
When the compression is horizontal the crust will be shortened and thickened. When the compression is vertical maximum a section of rock will fail in normal faults, horizontally extending and vertically thinning a given layer of rock.
