The oldest rock layer is the top layer of the cross section.
The oldest rock layer is the top layer of the cross section.
The oldest rock layer is above the bottom layer of the cross section.
The oldest rock layer is above the bottom layer of the cross section.
The oldest rock layer is the bottom layer of the cross section.
The oldest rock layer is the bottom layer of the cross section.
The oldest rock layer is above the middle layer of the cross section.