COSMIC-RAYS ABOVE 4 X 10(19) EV

An analysis is made of the distribution with Galactic latitude of cosmic rays of energy above 4 x 10(19) eV from the standpoint of determining whether they are of Galactic or Extragalactic origin. Although it is commonly argued that these particles are obviously extragalactic in origin, because of the near isotropy of arrival directions, in fact this could be accommodated by assuming a Galactic origin and a composition of heavy nuclei. However, using new calculations of panicle trajectories for a variety of field models we argue that the measured latitude distribution is inconsistent with this hypothesis, whatever the charge or (reasonable) magnetic field and source distribution. Thus, these particles are indeed mainly extragalactic and are, presumably, mainly protons, although, as is pointed out, there are some problems even with this hypothesis.