from Garner's Modern American Usage: continual = frequently recurring; intermittent. Continuous = occurring without interruption; unceasing. So if you wake me up with an air horn every morning, that's a continual annoyance. If you kept an air horn going off near my head 24 hours a day for a solid week, that would be a continuous annoyance.

I should note that the air horn example did not come from Garner.

viz: contiguous.