Marie Anne,
Thanks very much for that info, I shall investigate further.
These have been in dads collection for years, he thinks there American, a dealer friend of his thinks they maybe from Belgium or France but after handling them I think they are very similar in feel and material to the other Davidson and Greener opal pieces he has. I think it's the unusual rough base that is a bit off putting. Especially when they have gone to the trouble to include nice scrolled feet.
Greener made some nice lidded butter dishes in a cow pattern, there's one on eBay in malachite at the moment, that's why I think it maybe Greener?
Cheers