Three types of stone are shown in this view.
The local sarsen from the Marlborogh Downs, 20 miles to the north, a blue stone from the Prescelly Mountains of Pembrokeshire and the Altar Stone, which is a fine-grained pale green sandstone.
This, interestingly enough, is not in the Prescelly Mountains of Pembrokeshire, the source of the rest of the blue stones, but in the Cosheston Beds (a division of the Old Red Sandstone of South Wales) which crop out on the shores of Milford Haven, further south in the same county.
No other stone composed of this rock is known at Stonehenge, though occasional fragments of it, very probably detached from the Altar Stone itself, have been found in the soil of the site.
Significantly, chips of an entirely different grey-green micaceous sandstone have also been collected on the site, and have been identified with a particular outcrop of the Cosheston Beds at Mill Bay on the south shore of Milford Haven, about 2.5 miles above the ferry at Pembroke Dock.
