'if the buyer says nay'
Rather puzzling—doesn't Morris mean the 'seller'? Not if we realize the role of the sheriff here; he's an important local authority, one who mediates between foreign merchants (here the Scots speculators in horse-flesh) and the local farmers. He handles the money and keeps a tally for the farmers who raised the horses. More than a hundred sheriffs, 'syslumenn,' were scattered across Iceland's 18 counties, or 'syslar.'
'nice-looking little beasts'
See above, 'the little beast' under Friday, July 14.
'(the Springs--remember Ingjald of the Springs in Njala)'
The subject of the imperative, 'remember' is Georgiana. Morris is inviting her to recall a character in Njals Saga, which—in Dasent's translation—they'd evidently read together. Morris tells her--a few years later, in an 1877 letter--that he'd been reading the Njala in the original, and 'it is better even than I remembered; the style most solemn (Dasent now and then uses a word too homely I think, which brings it down a little): all men's children in it, as always in the best of the northern stories, so venerable to each other, and so venerated: and the exceeding good temper of Gunnar amidst his heroism, and the calm of Njal: and I don't know anything more consoling or grander in all literature (to use a beastly French word) than Gunnar singing in his house under the moon and the drifting clouds: or do you remember the portents at Bergthorsknoll before the burning, or how Skarphedinn takes them? Or Skarphedinn's death; or how Flosi pays the penalty for the Burning, never appealing against the due and equal justice, but defending himself and his folk stoutly against it at every step. What a glorious outcome of the worship of Courage these stories are.' See Mackail, vol 1, p. 335, and Kelvin, vol 1, p. 344. We must be pleased that Mackail preserved such heart-felt and wonderful appreciations of the greatest of the Family sagas, proof of Morris's critical acumen, as well as the depth of his friendship for Georgiana. He is confident that she shares his love for the Njala, and that she would appreciate every word of the IJ.
'on the way the old fellow'
These homey touches, for the benefit of Georgiana, make Morris's Journals unique among the few dozen 19th century travelers' accounts of Iceland. And note here also that WM must have gotten fairly adept at speaking Icelandic.