Obtain three Anti-Abyssean grenades from Fontoumant.
Travel to three Dark Fissures and toss in the grenades to destroy the Abyssean threat.
One of the Dark Fissures (H-6) is located on the valley floor in the same chasm as the Central Encampment; travel further down the ramp and look for a group of Pasture Funguars, nearby is the Dark Fissure.
The other two Dark Fissures are located in the chasm at (F-6) & (F-7), the same chasm which would normally lead to Ordelle's Caves, travel to the valley floor once more and continue on the pathway to Ordelle's Caves, along the way you will see two Dark Fissures.
Occasionally when using the anti-Abyssean grenades on the Dark Fissures, you may receive a message declaring that you have destroyed one of the Abyssean creatures residing inside; you will receive experience points (~221-350) for the monster you destroyed. The probability of this event is unknown; however, it is not necessary for completion of the quest.
Defeating a monster gives the following text, even if damage display in the log is turned off: (Name) casts anti-Abyssean grenade #0X into the fissure. The anti-Abyssean grenade scores a critical hit! The unidentified creature takes 9999 damage. (Name) defeats the unidentified creature. (Name) gains 350 experience points.