The puzzle of tectonic sliding is illustrated by means of the Roberts Mountains overthrust in north-central Nevada. A model of the thrust, consisting of a wedge-shaped sheet gliding into a subsiding and migrating basin of deposition, is described, and calculations are made for the requisite coefficient of sliding friction assuming only normal pore-water pressure (answer, $\mu = .08$) and for the requisite pore-water pressure under the whole thrust sheet, using a coefficient of internal friction for typical rocks, according to the Hubbert-Rubey hypothesis (answer, $\lambda = .93$). Neither result is attractive, and attention is turned to the premises of friction. Recent observations and hypotheses on mechanisms of sliding for metals and at least some non-metals emphasize the interdependent role of stresses normal and tangential to the sliding plane in creating and rupturing adhesions or junctions between the surfaces. These junctions alone support the load and make up the true area of contact which commonl...