Stonehenge: Local Bluestones from the west

I am far from being an expert on the geology of Somerset and Wilts, but on looking at the geology maps I am encouraged to do a bit of speculation. Let's refer to everything at Stonehenge that is not sarsen stone as BLUESTONE, since that's what people have been doing for years. There are hundreds if not thousands of bluestones of all shapes and sizes at Stonehenge that could well have come from the west and north-west, within 80 km of Stonehenge, and which could well have been carried by ice, if it did indeed come in from the Bristol Channel in the direction(s) discussed in earlier posts. So which "local" rock types might we expect to be represented in the Stonehenge bluestone assemblage? Look at the map and key above.

For a start, we might expect erratics of Upper Greensand, Corallian, Portland beds (Upper Oolite), Middle and Lowe Oolite beds (including some limestones and some sandstones), Upper Triassic beds (marls, sandstones, conglomerates), Carboniferous Limestone (from the Mendips) and even Coal Measures (mostly sandstones and shales, with interspersed coal-bearing beds). There are also a few outcrops of Old Red Sandstone on the flanks of the Mendips, to the west of Bristol and along the North Devon Coast -- and a few small exposures of igneous rocks too. I have forgotten here about the clay beds, on the assumption that they would not have contributed large blocks and monoliths to an erratic load or a till cover (they would have been broken down for the most part into silt and clay fractions). In short, sandstones, gritstones, and limestones galore COULD have been entrained, transported and finally dumped by overriding ice from the west.

There are lots of all of these rocks at Stonehenge, but archaeologists have tended to assume (a) that they have been imported manually by the Stonehenge builders, and (b) that they have therefore come from quite close at hand -- ie from the Vale of Wardour or from the Eocene outcrops to the south of Salisbury Plain's chalk downlands.

Here is a question for the geologists: Have any of these "local bluestones" found at Stonehenge been definitely fixed to the rock outcrops to the south or south-west of Stonehenge, or could they equally well have come from the west or north-west? Chilmark, in the Vale of Wardour, is often mentioned as an Upper Greensand source for "Chilmark stone" -- but is that just wishful thinking on the part of geologists and archaeologists who had no great desire to look for sources further afield, or in another direction?