On several occasions on this blog I have tried to publish a comprehensive list of all of the erratic or foreign stone types found at Stonehenge and in the immediate environs. I came up with a list of more than 30 rock types, which means more than 30 different provenances.....
Myris has recently reminded us that MPP is off hunting for Neolithic quarries again, and that he has had detailed discussions with the geologists as to where these might be. I would argue that that is a total waste of time and taxpayer's money, but I doubt that he will be deterred. So how many quarries are needed to satisfy an archaeologist who lives with the utter conviction that glacier ice had nothing to do with Stonehenge? I would say that we need at least 30 of them, since we do not just have to explain the presence of orthostats but also the presence of "debitage" (such as the debitage traced to Rhosyfelin) and other lumps of stone of various shapes and sizes. Rob would argue that we should dismiss all of this ancillary or incidental material and concentrate on the orthostats -- and he argues on that basis that all we need to find would be about ten quarries. I part company with him on that -- debris and foreign stones MUST be accounted for, whether they have been carried into the area by glacier ice, human beings or even machines involved in road-building works. (I have the same problem on Pembrokeshire beaches, trying to work out what might have been carried by ice and what might be dumped ship's ballast from the grand old days of sail.....)
So -- ten quarries, or thirty, or somewhere in between? And what are the features on the ground that we need to be able to identify in order to call a rocky outcrop a Neolithic quarry? We have had much discussion on this site about THE bluestone quarry at Carn Meini -- now, from what Rob is suggesting, Rhosyfelin is likely to be given similar star treatment. First will come a picnic site on the river bank -- then how about an interpretation panel and maybe a tasteful snack bar?
Here is the bluestone list published on this blog in 2010. It is as reliable as I can make it -- it it has any errors, please let me know. I will adapt and add notes as necessary. With a suitable input for geologists, I hope it can be refined to the point of becoming reliable and maybe even definitive.
Known Stonehenge Bluestone Types
1. Unspotted dolerite ---- monoliths 45 and 62. Carn Ddafad-las?
2, Spotted dolerite -- densely spotted. Monolith 42 -- Carnbreseb? 43?
3. Boles Barrow dolerite -- spotted? But similar to stones 44 and 45? From Carnmeini / Carngyfrwy area?
4. Rhyolite -- stones 38, 40, ignimbrite character. Ash-flow tuffs (dacitic). Not Carnalw ? May be from different sources?
5. Rhyolite -- stones 46 and 48, rhyolitic ash-flow tuffs. Carnalw area? Same source?
6. Rhyolite fragment from a different source from the above types
7. Laminated calcareous ash -- stumps 40c, 33f, 41d
8. Altered volcanic ash -- stump 32c, 33e?
9. Rhyolite -- another type -- stump 32e. Related to Pont Saeson samples? (Note added: This is the foliated rhyolite described from Rhosyfelin by Ixer and Bevins -- but the link with stump 32e is speculative, being based on photographic rather than rock sampling evidence.)
10. Micaceous sandstone -- stumps 42c, 40g (Palaeozoic -- South Wales origin?)
11. Rhyolite -- lava -- stone 46
12. Rhyolite -- flinty blue -- different lava? stone 48
13. Spotted dolerite with whitish spots --stones 33, 65, 68, stump 70a?, stump 71?, 72
14. Spotted dolerite with few spots -- stone 31, 66?
15. Spotted dolerite with pinkish spots -- stones 150, 32, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70
16. Spotted dolerite -- moderate spots -- stone 37, 61, 61a?
17. Unspotted dolerite -- stone 44 -- different from stones 45 and 62
18. Very fine-grained unspotted dolerite -- stone 62
19. Silurian sandstone -- Cursus -- fragments
20. Devonian sandstone -- Altar Stone -- Devonian Senni Beds -- Carmarthenshire or Powys
21. Sarsen sandstones -- various types -- packing stones and mauls
22. Jurassic oolitic ragstone -- Chilmark?
23. Jurassic glauconitic sandstone -- Upper Greensand?
24. Gritstone unspecified fragments (Maskelyne, Judd)
25. Quartzite unspecified fragments (Maskelyne, Judd)
26. Greywacke unspecified fragments (Maskelyne, Judd)
27. Granidiorite -- Amesbury long barrow 39
28. Quartz diorite -- ditto
29. Hornblende diorite -- ditto
30 Flinty rhyolite -- fragments from Pont Saeson (Note: different from the Rhosyfelin samples?)
31. Rhyolite fragments -- with titanite-albite intergrowths (source unknown)