We have measured the proton-air inelastic cross section at s 1/2 =30 TeV by observing the distribution of extensive-air-shower maxima as a function of atmospheric depth. This distribution has an exponential tail whose slope is ë = 72 ± 9 g cm-2 which implies that ó tot p-air= 530 ± 66 mb. Using Glauber theory and assuming that the elastic-scattering slope parameter b is proportional to ó tot pp , we infer a value of ó tot pp =120 ± 15 mb which lies between a log 2 s and a loges extrapolation of the total pp cross section as measured at lower energies.

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We report on a search fordeeply penetrating particles in the >1017 eV cosmic ray flux. No such events have been found in 8.2x106 sec of running time. We consequently set limits onthe following: quark-matter in the primary cosmic ray flux; long-lived, weakly interacting particles produced in p-air collisions; the astrophysical neutrino flux. In particular, the neutrino flux limit at 1017 eV implies that 3, the red shift of maximum activity is <10 in the model of Hill and Schramm6.

Extensive air-shower trajectories and sizes (numbers of charged particles) have been measured using an optical detection system at Volcano Ranch Station near Albuquerque, New Mexico. Light produced by atmospheric scintillation and Cherenkov emission by shower particles was measured at distances of 0.7 to ~ 10 km. The shower sizes determined by the optical measurements are in satisfactory agreement (an average of 10% higher) with measurements by the ground-level scintillation-counter array at Volcano Ranch.