As ever Branwen ... you go where angels fear to tread. Good on you.

I am waiting for a dental appointment and to take my mind off a throbbing tooth I took down my copy of "Irish Druids and Old Irish Religions" by James Bonwick. Here is an extract:

Stone Worship
In many lands shapeless stones have been adored. Among several ancient nations the idea of Divinity was symbolized by a rough stone. That aerolites should be revered is not surprising, since they, as the idol stone of Ephesus, came down from heaven. A single pillar stone might well, in rude times, typify a generative force. Jupiter, Apollo, Venus, Mercury, and Diana Patroa were adored as stone columns. A circle of upright stones has been reverenced from the Pacific, across the Old World, to the Atlantic …

It has been customary to call circles, cromlechs, Logan stones, pillar stones, serpentine and alignment stones by the appellation of Druidical. As these however are found in Japan, China, India, Persia, Arabia, Palestine, Barbary and every country in Europe, North and South America as well as in the Pacific Isles, it would imply certainly a very wide range of Druids. No one would deny that that in some parts, as Brittany and the British Isles, so-called Druids probably used such stones, as being already objects of reverence, without crediting them either as their builders, or as the originators of Stone Worship.

He also writes a chapter called:
The Culdees of Druidical Days which I have yet to read.
The first (pre-Roman) Christians had many similarities with the druids of the day. I am sure you know Branwen, Iona is still called the Druid's Isle by Highlanders and the Druids undoubtedly posessed it before it the introduction of Christianity.