We're building a natural rock walkway up to our front door. The walkway will be bordered by treated timbers. We collected the rocks (flat on one side, different heights and sizes, some quite large-1.5' x 1', average width- about 1.5"). Using instructions from a rock building book that says once the area is dug out, use gravel for the first layer,then sand to fill gaps once rocks are laid. We dug it out and it is clay underneath. Hubby thinks we don't need gravel because of the clay. Do we need gravel and what type of gravel? Book doesn't say. Thanks in advance for any help!