  The energy spectrum of the primary cosmic radiation in the energy range 1 -
100 PeV and the extensive air shower (EAS) characteristics obtained on the
basis of the expanded data bank of the GAMMA experiment (Mt. Aragats, Armenia)
are presented. With increased statistics we confirm our previous results on the
energy spectrum. The spectral index above the knee is about -3.1, but at
energies beyond 20 PeV a flattening of the spectrum is observed. The existence
of the 'bump' at about 70 PeV is confirmed with a significance of more than
4{\sigma}. In the energy range of 10 - 100 PeV the shower age becomes energy
independent and we observe a direct proportionality of the EAS size to the
primary energy. This suggests an approximately constant depth of the EAS
maximum in this energy range. This is evidence in favour of an increasing
average mass of primary particles at energies above 20 PeV. The additional
source scenario, which is a possible explanation of the 'bump' in the spectrum,
also leads to the conclusion of increasing mass of the primary cosmic rays. A
comparison with the data of other experiments is presented.
