" And the rocks melt wi’ the sun:..."
See in text (A Red, Red Rose)
“Wi’” here is an abbreviated form of “with,” but in this context would mean “under” or “from”: the rocks melt from the heat of the sun. This line is similar to the last one in the second stanza: if the speaker is being straightforward and genuine in the poem, this line reads as a hyperbolic statement meant to emphasize his commitment to his lover. If he’s being ironic, this line will read as an absurd over-exaggeration that really implies that love isn’t permanent, that it will pass. In the latter case, the visual image of rocks melting from the heat of the sun takes on an additional metaphorical layer. Under the heat of the sun, the seemingly unburnable rocks melt away; in the heat of passion, the seemingly endless love actually burns up and disappears.