rwise, restrict features to only things in the brush extent.
            filter = function(feature) {
                return feature.properties.time > +brush.extent()[0] &&
                    feature.properties.time < (+brush.extent()[1]);
            };
        }
        var filtered = data.features.filter(filter);
        earthquakesLayer.clearLayers()
            .addData(filtered);
    }
}
</script>
