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.

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