If the two hands be placed flat upon the table, in the angle between the two books, and the cloth pushed towards the corner, it will at once be rucked up into a fold which will follow a curve not unlike that of the Alps.
The rucked carpet or carelessly placed rug, long toenails, no stair rail, poor footwear, poor lighting.
The formation was dug down slightly where it had become rucked up and then the sleepers were laid out.