  It is proposed that the highest energy $\sim 10^{20}$eV cosmic ray primaries
are protons, decay products of a long-lived progenitor which has propagated
from typically $\sim 100$Mpc. Such a scenario can occur in e.g. SU(15) grand
unification and in some preon models, but is more generic; if true, these
unusual cosmic rays provide a window into new physics.
