How did the industrial revolution in England offer an example of natural selection?

One of the classic instances of natural selection is regarding the moths of industrial zones of England in the end of the 19th century and the beginning of the 20th century. Since the industrial revolution advanced the bark of the trees that moths landed on became darker due to the soot released from factories. The population of light moths then reduce and was substituted by a population of dark moths since the mimicry of the dark moths in the new environment protected them from predators that is they had an adaptive advantage in that new environment. The Light moths in their turn suffered the negative effect of natural selection for becoming more visible to predators and were almost eliminated. In the open forest far from factories though it was experimentally verified that light moths maintained their adaptive advantage and the dark moths continued to be more easily found by predators