=33-34. VT, QVA REMVS ITER PVLSIS MODO FECERAT VNDIS, / SICCVS CONTEMPTA NAVE VIATOR EAT.= Ovid has in mind Virgil's description of the freezing of a Scythian river (_G_ III 360-62) 'concrescunt subitae currenti in flumine crustae, / undaque iam tergo ferratos sustinet orbis, / puppibus illa prius, patulis nunc hospita plaustris'. =35. QVI VENIVNT ISTINC VIX VOS EA CREDERE DICVNT; / QVAM MISER EST QVI FERT ASPERIORA FIDE.= For Ovid's fear that his accounts of what he has undergone will not be believed, see vii 3-4 and _Tr_ I v 49-50, III x 35-36 & IV i 65-66. In particular, see ix 85-86 'mentiar, an coeat duratus frigore Pontus, / et teneat glacies iugera multa freti'. =37-38. NEC TE CAVSAS NESCIRE SINEMVS / HORRIDA SARMATICVM CVR MARE DVRET HIEMPS.= Ovid's principal explanation of the freezing of the Euxine, the low salinity of the water, is found in four other Latin authors. At IV 718-28, Valerius Flaccus offers a catalogue of rivers similar to that of Ovid, and, like Ovid, gives the cold winter winds as a subsidiary reason for the freezing. It is quite possible that Ovid is Valerius' source; but this is very unlikely to be the case for Macrobius _Sat_ VII xii 28-38 (cited by Burman). The passage is a discussion of why, although oil congeals, wine and vinegar do not. Wine does not freeze because it contains elements of fire; this is why Homer called it [Greek: aithopa oinon]. Vinegar does not freeze because it is so bitter; it is like seawater, which because of its bitterness does not congeal. 'nam quod Herodotus historiarum scriptor contra omnium ferme qui haec quaesiuerunt opinionem scripsit [IV 28], mare Bosporicum, quod et Cimmerium appellat, earumque partium mare omne, quod Scythicum dicitur, id gelu constringi et consistere, aliter est quam putatur'. It is not the seawater that freezes, but the layer of fresh water above it, which comes from the rivers that flow into the Euxine. Macrobius goes on to explain that there is an outflow of fresh water to the Mediterranean and an influx of seawater, with perfect correctness: the _Encyclopaedia Britannica_ article cited at 32 notes that 'Flows in the Bosporus are complex, with surface Black Sea water going out and deep, saltier water coming in from the Sea of Marmara*.