  Project GRAND presents results on the atomic composition of primary cosmic
rays. This is accomplished by determining the average height of primary
particles that cause extensive air showers detected by Project GRAND. Particles
with a larger cross sectional area, such as iron nuclei, are likely to start an
extensive air shower higher in the atmosphere whereas protons, with a smaller
cross section, would pass through more air before interacting and thus start
showers at lower heights. Such heights can be determined by extrapolating
identified muon tracks backward (upward) to determine their height of origin
(Gress et al., 1997). Since muons are from the top, hadronic part of the
shower, they are a good estimator for the beginning of the shower. The data for
this study were taken during the previous year with 20 million shower events.
