The riddle of sand

The fractal nature of sand - a theme that draws me back, time and time again. The forms that it takes remain remarkably similar across a wide range of scales, from a ripple on the beach, to the mighty dunes of the Empty Quarter. William Blake put it beautifully in his 1803 poem Auguries of Innocence:

To see a world in a grain of sand,
And a heaven in a wild flower,
Hold infinity in the palm of your hand,
And eternity in an hour.
........

William Blake