In the first photo the eastern end of the Altar Stone is seen to the left of Stone 55b, the middle section is visible between Stone 55b and Stone 156 and the western end is out of shot to the right of Stone 156.
The eastern end:
The middle section between Stone 55b and Stone 156:
The western end beneath Stone 156:
Stone 80 is of Type: Sandstone (Devonian)