Erosion being the wearing down of a hard substance, it symbolizes submission to higher spiritual forces or principles. Extreme emotion can be very wearing, so often when we are under stress we can dream, for instance, of a river eroding its banks or of the sea wearing away a cliff. Such an image can suggest that, by perseverance, we are able to overcome difficulties. There may not be an immediate solution to a problem, but by working away at it, it can be solved. You might also like to consult the entry for Cliff.