Mine

                for (int i = 0; i < MapEngine.myMap.mapWidth; i++)
                {
                    for (int j = 0; j < MapEngine.myMap.mapHeight; j++)
                    {
                        // Make the copy
                        tempLayer[0, i, j] = MapEngine.myMap.MapLayers[oldIndex, i, j];
                        MapEngine.myMap.MapLayers[oldIndex, i, j] = null;

                        // Change the new one the old one
                        MapEngine.myMap.MapLayers[newIndex, i, j] = MapEngine.myMap.MapLayers[oldIndex, i, j];

                        // Change the old one to the new one
                        MapEngine.myMap.MapLayers[oldIndex, i, j] = tempLayer[0, i, j];
                    }
                }