  We report an estimation of the injected mass composition of ultra-high energy
cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is
inferred from an energy-dependent sky distribution of UHECR events observed by
the Telescope Array surface detector by comparing it to the Large Scale
Structure of the local Universe. In the case of negligible extra-galactic
magnetic fields the results are consistent with a relatively heavy injected
composition at E ~ 10 EeV that becomes lighter up to E ~ 100 EeV, while the
composition at E > 100 EeV is very heavy. The latter is true even in the
presence of highest experimentally allowed extra-galactic magnetic fields,
while the composition at lower energies can be light if a strong EGMF is
present. The effect of the uncertainty in the galactic magnetic field on these
results is subdominant.
