  A brief review of the energy spectrum of primary cosmic rays above $10^{10}$
eV and the measurement techniques used to investigate the ultra high energy
ones is given. This is followed by a discussion of the atmospheric shower
profile of the highest energy event observed using the Fly's Eye detector.
Finally, cosmic ray simulation tools are discussed and used to investigate the
heavy ion interpretation of the highest energy primary. The best way to
contribute further to the understanding of this issue is by the collection of
new and better data.
