var layer = maxLayers = c = 0;    
$(document).ready( function() {
    $('div.banner').each( function(i){
      c++;
      //Assign indexes, and ID's dynamically in appearance of DOM objects
      $(this).attr('id', 'z'+c);
      $(this).css({'z-index': c });
    });
    maxLayers = c; //set to length of banners
    setInterval("bannerSwitch();", 5000);
});

function bannerSwitch(){
    layer++;
    if(layer > maxLayers){
      //restart, hide last layer go back to start
      $('#z'+(layer-1)).fadeOut('slow');
      layer = 0;
      return;
    }else{
      //Fade in, then hide old layer underneath
      $('#z'+layer).fadeIn('slow', function(){
          if(layer != 1) $('#z'+ (layer - 1)).hide();
      });
      return;
    }
}