imbricated rock

Rocks are imbricated when their edges overlap, like roof shingles or the scales on a Douglas fir cone. (The Latin root is imbrex, a curved tile.) For a geologic sense of the range of the term, imagine very big imbrication (overriding land masses piling up like slumped stacks of giant pancakes); odd, scary imbrication (boulders layered on a coast, likely dominoed there by the wave action of a tsunami); and streambed imbrication (cobbles overlapping and angled by moving water). Imbricated rock lets you hold solid and see fluid. In a stratum of fluvial sandstone, water-worn cobbles pile edge over edge in a shingle pattern, their long axis aligned with the current. Such dipped and titled cobbles imply paleo-currents, the direction of flood and deposition in a river that flowed millions of years ago.

Ellen Meloy