x & y data timeseries wont stack

why do these not stack?

> `var chart = c3.generate({
> data: {
> xs: {
> tag0: 'xtag0',
> tag1: 'xtag1',
> tag2: 'xtag2'
> },
> columns: [
> ['xtag0',"2012-2-18","2012-3-18", "2012-10-18" ],
> ['tag0', 30, 100, 200],
> ['xtag1', "2012-4-18","2012-5-18", "2012-10-13"],
> ['tag1', 20, 75, 80],
> ['xtag2', "2012-6-18", "2012-09-13", "2012-10-13", "2012-11-13"],
> ['tag2', 50, 250, -5, 150]
> ],
> types: {
> tag0: 'area-spline',
> tag1: 'area-spline',
> tag2: 'area-spline'
> },
> groups: [['tag0', 'tag1', 'tag2']]
> },
> axis: {
> x: {
> type: 'timeseries'
> }
> }
> });`