Merging overlapping ranges in PHP arrays?

I have an array in the following format:

array(
  0 => array(1, 5),
  1 => array(4, 8),
  2 => array(19, 24),
  3 => array(6, 9),
  4 => array(11, 17),
);

Where each item is a X-to-Y range. What I would like to merge the overlapping ranges in the array, to get something more like this:

array(
  0 => array(1, 9), // 1-5, 4-8 and 6-9 are overlapping, so they are merged
  1 => array(11, 17),
  2 => array(19, 24),
);

What would be the best way to accomplish this?