  Cross sections for elastic photoproduction of J/Psi and Upsilon mesons are
presented. For J/Psi mesons the dependence on the photon-proton centre-of-mass
energy W_gammap is analysed in an extended range with respect to previous
measurements of 26<=W_gammap<= 285 GeV. The measured energy dependence is
parameterized as sigma_gammap proportional W_gammap^delta with
delta=0.83+-0.07. The differential cross section dsigma/dt for J/Psi mesons is
derived, its dependence on W_gammap and on t is analysed and the effective
trajectory (in terms of Regge theory) is determined to be
alpha(t)=(1.27+-0.05)+(0.08+-0.17)*t/GeV^2. Models based on perturbative QCD
and on pomeron exchange are compared to the data.
