[en] Magnetic spectrograph measurements are presented of the intensities of cosmic ray muons reaching sea level with arrival directions inclined at 30⁰ and 75⁰ to the zenith. The range of momenta covered by the measurements extends from 50 GeV/c to beyond 1000 GeV/c. The ratio observed between the intensities of positive and negative muons leads to the conclusion that about half of all primary nucleons with energies of around 2 x 10¹² eV are neutrons. This implies that about one-third of all primary nucleons at these energies are bound in nuclei; and measurement of the angular variation of the muon flux supports this conclusion. These results indicate that some heavy-element primaries must display spectra that are significantly flatter than the spectrum of primary protons up to nucleon energies of several times 10¹² eV. Direct measurements of the primary spectrum have verified flatter spectra for iron and several other heavy elements at energies below 10¹¹ eV. Results extend the findings of the direct measurements by about two orders of magnitude in nucleon energy