como fazer elementos que scroll diferente

1$(window).scroll(function(e){
2  parallax();
3});
4function parallax(){
5  var scrolled = $(window).scrollTop();
6  $('.bg').css('top',-(scrolled*0.2)+'px');
7}

1.bg {
2  background: url('http://i.imgur.com/USFbNpC.jpg') repeat;
3  position: fixed;
4  width: 100%;
5  height: 300%;
6  top:0;
7  left:0;
8  z-index: -1;
9}
10section {
11  color: #fff;
12  font-family: arial;
13  width: 500px;
14  margin: auto;
15  line-height: 20px;
16  font-size: 16px;
17}