When a stratum of rock is tipped by tectonic forces, earth scientists characterize its orientation to the surface of the Earth—imagining the surface as a horizontal line—in terms of its dip and strike. If a layer of rock is tipped forty degrees below the horizontal, it would have a dip of forty degrees. If the slope faced south, its strike would be east-west, the orientation of a line perpendicular to the line of its dip. If a person were characterizing, in this instance, a particular sandstone outcrop, he’d say, “This layer of sandstone has a dip of forty degrees to the south and its strike is east-west.” If an uplifted layer of rock buckles, creating a ridge parallel to its strike, that would be a strike ridge. If a river eroded a valley in a line parallel to the strike of the rock it was eroding, that would be a strike valley. If a layer of rock fractures into two blocks and one slides past the other horizontally, it’s a strike fault. The word strike has nearly eight dozen meanings. There’s little reason to believe that the straight path of a strike valley, its determined direction, gave rise by itself to the expression “to strike out on one’s own,” but a strike valley beckons in a way a tortuous valley does not.