Work in progress.........
There are nineteen visible stones in the Bluestone Circle and also assorted buried stumps. Here is an attempt at itemising the full list, with reference to stone shapes, surface characteristics and petrology:
31 -- damaged and heavily worn slab. Standing. Recent damage close to ground level. Spotted dolerite with few spots.
32 -- heavily worn slightly elongated boulder. Fallen -- resting on stone 150. Spotted dolerite with pinkish spots -- like stones 150, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70
32c -- altered volcanic ash. Like 33d. Foliated rhyolite related to Rhosyfelin debitage?
32d -- another foliated rhyolite stump? Related to Rhosyfelin material?
32e -- Dolerite stump -- characteristics unknown
33 -- well worn short and stumpy pillar. Standing. Signs of shaping -- meant as a lintel? Spotted dolerite with whitish spots.
33e -- altered volcanic ash (stump). Like 32c
33f -- altered volcanic ash (stump). Laminated -- like 40c and 41d
34 -- well rounded small boulder, placed on end. Spotted dolerite with pinkish spots -- like 32?
35 a and 35 b -- irregular and well worn boulder, embedded in the ground and only just visible. Spotted dolerite with pinkish spots -- like 32?
36 -- an irregular and heavily worn boulder, slightly elongated. Modern damage on one edge. Recumbent
37 -- smallish well-rounded boulder, slightly slab-shaped and set on end. Spotted dolerite with moderate spots.
38 -- smallish irregular boulder, well worn, fallen and under another stone. Rhyolite, ignimbrite. Dacitic ash-flow tuff.
39 -- another smallish boulder, well worn, slightly slab-shaped, with some later damage. Leaning, almost recumbent. Spotted dolerite with pinkish spots -- like 32?
40 -- Rhyolite, ignimbrite. Dacitic ash-flow tuff. Stump beneath ground? Laminated -- like 33f and 41d?
40c -- stump. Laminated calcareous ash
40g -- below ground stump -- irregular shape. Micaceous andstone. Lower Palaeozoic?
41 -- recumbent elongated boulder with heavy wear -- very well rounded edges
41d -- stump. Altered volcanic ash. Laminated -- like 33f and 40c
42 -- recumbent wedge-shaped stone with heavy wear on edges. Densely spotted dolerite?
42c -- stump. Sandstone (micaceous). Lower Palaeozoic?
43 -- recumbent slightly flattened boulder with heavy wear on edges. Densely spotted dolerite?
44 -- heavily worn boulder just visible in the turf -- recumbent. Spotted dolerite? Similar to Boles Barrow dolerite?
45 -- recumbent elongated boulder with heavy wear on edges. Unspotted dolerite? Different from 44.
46 -- slightly slab-shaped boulder set on edge. Flaky -- considerable recent surface damage. Rhyolitic ash-flow tuff like stone 48? Or is it a lava?
47 -- slab with heavy wear on edges -- set on end. Spotted dolerite with pinkish spots -- like 32?
48 -- small recumbent boulder with heavy wear -- just projecting through the turf. Rhyolitic ash-flow tuff (flinty blue) but not like stone 46?
49 -- small irregular slab with quite sharp edges. Upright. Signs of dressing? Intended as a lintel? Spotted dolerite with pinkish spots -- like 32?
Note that there are at least a dozen dolerites in this collection -- so not all of the available dolerites were placed into the Bluestone Horseshoe. The dolerite slabs and boulders of assorted shapes and sizes were used in the Bluestone Circle, and the more elongated dolerites (the pillars) were used in the Horseshoe. So it can NOT be argued that the builders of Stonehenge were intent on collecting dolerite PILLARS from Preseli to the exclusion of all other dolerite shapes. Here they have used a weird assortment of dolerites of all shapes and sizes. As suggested in earlier posts, the presence of slabs, roughly rectangular blocks and boulders -- for the most part with rounded-off edges and corners and with an overall shape we will refer to as "sub-rounded" -- is highly suggestive of long-distance glacier transport. It is logical to assume that these stones (we won't call them "orthostats") are not simply glacial erratics but glacial erratics that have travelled a long way. In other words, they have in all probability been collected from Salisbury Plain or somewhere near it.
The OU team (which involved Olwen Williams-Thorpe and Rob Ixer) had consent from EH to sample 11 of the dolerite orthostats in the Bluestone Horseshoe and 4 of the "rhyolite" orthostats in the Bluestone Circle. that means that cores were taken. Were there any measurements and analyses of the weathering crusts revealed in these cores?