Some may remember from our youth the sad fate of Mary, she who was dispatched to call the cattle home across the sands of Dee:
The western tide crept up along the sand,
And o'er and o'er the sand,
And round and round the sand,
As far as eye could see.
The rolling mist came down and hid the land,
And never home came she.
But this cautionary tale illustrates only one kind of danger that may lurk in such a place. Sand can set other traps for the unwary: it may be quicksand.
Sand is most familiar to us in the guise in which we see it on the sea-shore - either dry and powdery, or hard-packed, damp and firm. Since the grains of which it is composed are irregular in shape and rough, they lock to support the weight of anything upon them.
But sand becomes "quick" - an archaic epithet which meant to "be alive" or "moving" - when water, usually up-welling from below ground, surrounds the individual grains, and fills the little gaps and spaces in between; then they cannot lock together, the sand behaves like liquid, and the only weight it can support is that determined by the principle of Archimedes.
Thus quicksand is most likely to be found where there are springs, where water falling on relatively high ground is carried downward through channels in the rock to surge up again at some lower level underneath an area of sand. It follows that quicksand is rarely found on flat countryside, or where the landscape has deep ravines and gorges into which the water drains. It is a phenomenon of a moderately hilly landscape of the kind where springs are common.
The plain truth is that any sand, with water added, becomes quicksand, and the secret of survival is "don't panic!" The mixture has a density of 1.6 or thereabouts, compared to 1.0 in the case of water, and about 1.02 for salt water from the sea.
It follows that anyone lying calmly on their back with arms outstretched will be supported even more effectively than if floating in the ocean. The difficulty, if you are trapped "feet first" in quicksand, is that it has a great reluctance to "let go"; to extract a limb, you have to fight against the vacuum left. But contrary to what it popularly supposed, quicksand does not suck people downwards; it will try to support them given half a chance.