What primary process leads to the formation of bays along a discordant coastline?

The primary process leading to the formation of bays along a discordant coastline is the erosion of weaker rocks. Discordant coastlines are characterized by variations in rock type, where harder, more resistant rocks alternate with softer, less resistant ones.

When waves approach these coastlines, they tend to erode the softer rocks more rapidly due to their lower resistance to wave action. Over time, this differential erosion causes the softer rock areas to recede, forming a bay where the harder rock protrudes outwards, creating headlands. The continual process of wave energy focusing on the weaker rock accentuates this erosion further, leading to the distinct coastal landforms typical of discordant coastlines.

Wave refraction plays a role in focusing wave energy, but it is the actual erosion of the rocks that is responsible for creating the bay itself. Friction erosion doesn't accurately describe the processes occurring at coastlines, and solifluction, which involves the slow flow of water-saturated soil down a slope, is not relevant to coastal landforms. Thus, the erosion of weaker rocks is the driving force behind the creation of bays in these environments.