  The existence of extra degrees of freedom beyond the electroweak scale may
allow the formation of black holes in nearly horizontal neutrino air showers.
In this paper we examine the average properties of the light descendants of
these black holes. Our analysis indicates that black hole decay gives rise to
deeply penetrating showers with an electromagnetic component which differs
substantially from that in conventional neutrino interactions, allowing a good
characterization of the phenomenon against background. Naturally occurring
black holes in horizontal neutrino showers could be detected and studied with
the Auger air shower array. Since the expected black hole production rate at
Auger is $> 1$ event/year, this cosmic ray observatory could be potentially
powerful in probing models with extra dimensions and TeV-scale gravity.
