  The small change in the spectral slope of the overall intensity of cosmic
rays near 1 PeV may be associated with the endpoint energy of supernova shock
acceleration. A crucial test of this connection and other ideas of the origin
of the spectral `knee' is the reliable determination of the variation of
elemental composition in this region. Recent measurements at the DICE/CASA/MIA
air shower installation in Dugway, Utah, USA have provided several independent
air shower parameters for each event. The derivation of elemental composition
from a combination of Cherenkov size, depth of shower maximum in the
atmosphere, muon size and electron size at ground level and the reliability of
these results are discussed. There is no evidence from these data for a large
change in the mean mass of cosmic rays across the `knee'. These measurements
show the cosmic rays are composed of ~ 70% protons and alpha-particles near
total energies of 10PeV.
