This author's nonsensical
This author's nonsensical only novel features a discourse on the utility of pockets and is marked by an unknown triangular symbol attributed to the Garamna people.  Sir Ralph the Rover comes upon the bell placed on the title outcropping by the Abbot of Aberbrothok in his "The Inchcape Rock," while Baly and Padalon are among the locales visited by the title character of his "The Curse of Kehama." In another poem, after Peterkin finds a human skull, Old Kaspar tells the story of the title conflagration.  Subjects of his long poems include Robin Hood, Joan of Arc, and a Welsh prince who legendarily discovered America in 1170.  Magicians from Domdaniel are dispatched to kill the titular "destroyer" of another poem, though better-known is a poem that inspired a parodic retort from Lord Byron.  For 10 points name this author of "Thalaba" and A Vision of Judgement, a Lake Poet who also wrote about the Battle of Blenheim.
This author's nonsensical only novel features a discourse on the utility of pockets and is marked by an unknown triangular symbol attributed to the Garamna people.  
Robert Southey