Pebbles on sand, continued

My photographer friend in Sweden, Olle Petterson, asked for an explanation of what the previous post, "pebbles on sand" was all about. I didn't mention that the pile of sand you see in this image was brought to the Bosque for the purpose of constructing sidewalks around the reception center. Santarém is blessed with a great variety of sands, each used specifically for some building purpose. There are red sands, white sands, fine grained sands, course grained sands and sands with lots of pebbles. Sand is the best filter to ever come our way. Water has a way of going through it very fast, which explains why our underground water is of such excellent quality in this Tapajós River region.