This article is from the Final-Fantasy and other Square Soft Games FAQ, by email@example.com (Nick Zitzmann) with numerous contributions by others.
It's actually not a dead end. There's a cleverly hidden passageway which
allows you to continue.
To see the passageway, arrive at the "dead end" room, then make one
character a Geomancer. There is a hole in the ground inside this room
which allows you to continue on your way.