  In recent years the Fly's Eye and Akeno groups have presented analyses of the
cosmic ray mass composition at energies above 10^17 eV. While the analysis of
the Fly's Eye group points to a likely change in mass composition from heavy to
light at energies above 10^18 eV, the Akeno analysis favours an unchanging
composition. However, the two groups base their conclusions on simulations
using quite different hadronic models. Here we present a comparison of the
experiments using the same hadronic model and find that the agreement between
the experiments is much improved. Under this model, both experiments measure a
composition rich in iron around 10^17 eV which becomes lighter at higher
energies. However, the agreement is not complete, which indicates scope for
improvement of the interaction model, or perhaps the need for a re-examination
of the experimental results.
