By close observance of these bands, we can read the recent storm history of East Beach as if we were reading the rings of a tree. The width of the bands, or lenses, as well as the color changes indicate the intensity of past weather patterns. Lighter tones represent gentler waves while the darker, more coarse sand lenses indicate severe storms. The reason for this is that the more powerful waves carry the heavier sediment further, depositing them on shore. It must be the magnetite and black mica we learned was part of the sand's composition.
Sand can be pretty different from place to place.
Now we know what causes that.