  Some recent measurements of the chemical composition of the cosmic radiation
indicate that at the energy of 3 x 10 **18 eV, around the ankle, light cosmic
ions dominate the spectrum as it occurs in the preknee energy region. Taking
advantage of a recent theory of cosmic radiation which provides a quantitative
explanation of the knee, the second knee and the ankle, the chemical
composition of cosmic radiation is explicitly calculated giving individual ion
spectra and ion fractions from 10 ** 12 eV to 5 x 10 ** 19 eV. The calculation
assumes two components of the cosmic radiation feeding the ion flux at Earth:
one originated in the disc volume and another one, called extradisc component,
which from the disc boundaries traverses the Galaxy reaching the solar system.
Data above 10 ** 17 eV collected during half century of experimentation by
Auger, HiRes, Agasa, Akeno, Fly' s Eye, Yakutsk, Haverah Park and Volcano Ranch
experiments are reviewed, examined and compared with the theoretical <ln(A)>.
The comparison between computed and measured <ln(A)> exhibits a good global
accord up to 2 x 10 ** 19 eV except with the HiRes experiment and an excellent
agreement in the range 10 ** 15 - 10 ** 17 eV with Kascade, Eas-top, Tunka and
other experiments. The accord requires a flux of the extradisc component of 1.8
x 10 ** 14 particles / m ** 2 sr s eV **(1.5) at 10 ** 19 eV, twice that
generated by disc sources.
