Unfortunately "Natural Sediment" is not what they tell you, Ive worked in many buildings in London and seen things like this, if only i was awake 25 years ago to expose it but everything happens for a reason.

What you have to ask yourself is what is Sand? what is under it? and why so much of it? Sand is more than you think, Research it, even look at it under a microscope. Everything isnt as it seems but as always it depends if you want to see it and believe it, Its up to each individual to look and question everything which has been told to us.