Hi True Owl,
The veneration of water sites and votive offerings does indeed go back a long time, a very long time and tossing a coin into a fountain or well for good luck is, I believe, a recollection of this.
We need to be careful not to read too much, too little or just what we want to into these things, but I’d say that given the veneration of water sites in pre-Christian Britain and Ireland and the “continuity” of the veneration of (holy) wells in Cornwall, but also in areas such as Derbyshire, there’s strong circumstantial evidence at least to give weight to the idea. In recent years there’s been a bit of academic controversy about the historiography of these sites and traditions, we just don’t have enough evidence going back far enough to be sure and some traditions were only recorded for the first time in the modern period, that’s not to say they didn’t exist before, but we just can’t say so with certainty. On the other hand, archaeological, i.e. material, data does indicate that a number of sites, for example Flag Fen, enjoyed an incredibly long history of devotion spanning different metal ages and cultural changes.
When the Romans came, native British spiritual belief merged with Roman belief and we had a form of Romano-British religion, for example, Sulis Minerva at Bath. It seems that British religion became Romanised quite rapidly. Then when Christianity came along, the native beliefs got mixed with Christian ideas and so on. I think one thing we should bear in mind is that the “high” religion of the elites, the urban upper classes, the aristocracy, the people who were literate is one thing whereas the “folk religion” of the pagani – the country dwellers – was probably something quite different and perhaps more conservative and naturally more tied to the seasons, agriculture, hunting, natural phenomena and the land and this is where our folk traditions originate. Just because a monk, a king or a scholar believed something or held a world view, doesn’t mean that it was shared by a shepherd on the moors who was probably still worried about bad weather, wolves and bandits!
Going back to Carn Marth, the hypotheses could be:
1) Ancient tradition – folk memory of when women and girls blessed by a female fertility goddess/divinity in spring.
2) Ancient tradition – the dolls were blessed as a form of sympathetic magic, maybe some connection to corn dollies, which was later forgotten.
3) Christian Easter tradition – the dolls were blessed, however, I have a doubt about this – baptism is an important sacrament and baptising dolls, well, I’m not sure how well – pardon the pun – that would sit with Christians in the past.
4) Just an old country folk tradition and game with toys/dolls, nothing to read into it.
5) Something else …