It is not always clear which author wrote which segment of the book, but the delight in the quirkiness of the Icelandic language which emanates from the following extract suggests Auden to me. The first four-line stanza (on the left) should of course be read from top to bottom (Falla .. daga), then it can be read in reverse (daga .. Falla) which replicates the stanza on the right.
In the second pair of stanzas, the one on the right is a translation (by Auden?) of the Icelandic original on the left.
They seem to have preserved a passion for ingenuity helped by their damnably inflected language, since the days of the Scald's [sic], whose verse would have broken St. John Ervine right up. Even now they write palindrome verses which can be read forwards or backwards, like this:
Falla tímans voldug verk Daga alla stendur sterk
varla falleg saga. Studla ríman snjalla
Snjalla ríman studla sterk Saga falleg varla verk
Stendur alla daga. voldug tímans falla.
Sentiment: Art is long and life is short or life is short and art is long. Or verses like this in which the second half is made up of the beheaded words of the first:
Snuddar margur trassin traudur Many a lazy idler lounger
Treinist slangur daginn And finds the day long;
Nudda argur rassin raudur The wicked one rubs his red bottom
reinist langur aginn. And finds discipline irksome.