Effect.ScrollContainer = Class.create(Effect.Base, {
  initialize: function(element,scroll_to) {
    this.element = $(element);
    this.scroll_to = scroll_to;
    if (!this.element) throw(Effect._elementDoesNotExistError);
    var options = arguments[2] || { };
    this.start(options);
  },
  setup: function() {
  	this.scroll_from = this.element.scrollTop;
  },
  update: function(position) {
    this.element.scrollTop = this.scroll_from + (this.scroll_to-this.scroll_from)*position;
  }
});