... implies that evolution did not proceed as presently envisioned. (Rocks are often dated by their fossil contents.) So, geologists are left with the problems of sliding great masses of rock over rough surfaces for great distances. Sketch of the forces acting upon a thrust block being pushed by a wedge-shaped driver Low-angle thrust faulting is not a trivial geological process. To illustrate, the Lewis Overthrust in Montana and adjacent Canada involves the shoving of a block of old strata hundreds of feet thick, hundreds of miles long, over younger rock for a distance of possibly 50 miles. In contemplating such overthrusts, one immediately comes face to face with the Mechanical Paradox. Brief-ly, given the coefficient of friction between the layers of rock, the weight of the thrust block, ... the mechanical strength of the rock being pushed, it can be shown that pushing the thrust block at the rear edge will crush it long before it begins to slide. For nearly a century, geologists have been trying to resolve this Mechanical Paradox. Three potential solutions have been proposed: (1 ) Lubricate the sliding surfaces with water under high pressure (the pore-pressure approach); (2 ) Allow the thrust block to slide, not as a unit, but in small discrete areas at different times (the dislocation approach); and (3 ) Push the thrust block not only from the rear edge but along the top surface (the tapered wedge approach). In fact, all three solutions may apply; but there is no consensus so far. Each solution has problems ...