Comment by pjc50

Deindustrialization, triggered by depletion. The thing about mines is they don't last forever, and if you build your industry near the mines that supply it it becomes uneconomic once the mine is depleted.

Also, the world got a lot bigger, to the extent that a tiny canal was no longer meaningful.

The population of Scotland as a whole has grown slowly and continuously - nothing comparable to the mass depopulation of Ireland, even when you consider the Highland Clearances. It has however mostly concentrated in the economic centers of Edinburgh and Glasgow.