The other sandstones

With ref to the recent discussion on the Altar Stone, I just recalled that there are 2 (at least) other sandstone monoliths in the bluestone circle at Stonehenge -- numbered 40g and 42c. They are conveniently forgotten about, because they are just represented as stumps, buried beneath the turf and now no longer visible.

Where have they come from? Well, four sandstone fragments (that may or may not be linked directly to these stumps) have been examined by Dr RG Thomas, Dr Rob Ixer and Dr Peter Turner -- and it turns out that they are not the same as the Altar Stone sandstone, and not from the Cosheston Beds. They may be Silurian sandstones, from western Pembrokeshire, Ceredigion or mid-Wales.