I’m generally rather sceptical of ‘place-name evidence’. But it seems that ‘generic’ stream names are, in aggregate, clear evidence of ancient territorial boundaries. Which is a very interesting finding…

One can glimpse here the boundaries of ancient Mercia, the incursion of the Danelaw, and even spot the English speakers who settled into a little nook of Wales. Tolkien was fascinated by that nook, as a linguistic reliquary, and is known to have visited it. In one of his texts he named himself ‘Prof. Rashbold of Pembroke’.