Which will float?

Today we completed our final mixture; woodchips, pebbles, and water.  We predicted which solid would float and then combined our mixture.  We stirred it up and allowed it to settle. Then we observed at eye level to determine which solid would sink and which would float.  The pebbles are more dense than the water, so they sank.  The woodchips were less dense, so they float.  We got our hands wet separating the mixture back to its original form.