FF2 help plz.

ok, im playing FF2 and i am in Deist cave. I am at the area where you cross the bridge but it collapses and you go down one floor. i have no idea where to go. after the bridge collapses i end up only able to backtrack up through the cave, or go forward to a dead end with a bunch of treasure chests i have already obtained. Can anybody please explain to me where to go? thanks.

EDIT: Ok, i no longer need help on this, but i do need help on something else. I am now in the basement of castle Phin, and i am on the fifth floor looking for the white mask and i can't seem to find it. The walkthrough on this site says it is down there, on the fifth floor but it doesnt seem to be anywhere. So if anyone could help me out on this it would be much appreciated. Thanks.