  We present arguments aiming at reconciling apparently contradictory results
concerning the chemical composition of cosmic rays of highest energy, coming
recently from the Auger and HiRes collaborations. In particular, we argue that
the energy dependence of the mean value and root mean square fluctuation of
shower maxima distributions observed by the Auger experiment are not
necessarily caused by the change of nuclear composition of primary cosmic rays.
They could also be caused by the change of distribution of the first
interaction point in the cascade. A new observable, in which this influence is
strongly suppressed, is proposed and tested.
