What would cause that layer of soil to become white?

Today I had my first lecture for AGRY 255: Intro to Soil Sciences. We dove right into the material and learned some basic terms and concepts behind soil science. One of the topics we glanced at was soil horizons. A soil horizon is a distinct layer of soil in a "vertical" sample (without pictures, I can't think of a better way to describe the type of sample). You can see these separate horizons, although some are more distinct than others. In one picture he showed us to emphasize the differences among soil samples there was a bright white horizon (which I now know to be the E horizon) between two healthy brownish horizons (the A and B horizons, as it were). I wondered what might cause such a stark white, so I stuck around to ask.

First off, it's lighter because it's an E horizon. The E stands for eluviate, which indicates that things are leeched out of that layer. Rain (or run-off or whatever) washes organic matter, minerals, and clays out of that horizon into the B horizon below. Minerals and whatnot are also washed out of the A horizon above, but organic matter from the surface is constantly replacing what is depleted and a a darker color is maintained. So all E horizons are lighter than the horizons above and below. But the contrast in this particular E horizon was rather extreme. It is likely that a strong acid was in the E horizon of the sample in question. This acid would further break down what little wasn't washed out and leave a white color behind.