I have devoted some space before to those strange features examined over the years by archaeologists and generally referred to as "periglacial stripes" -- and referred to, with delightful quaintness, as "geological stripes" or "natural Ice Age gullies" by EH. I've done a bit more digging into the literature -- a poor substitute for digging into the ground -- and I am increasingly convinced that they are not periglacial in origin.
Here are the latest EH statements about them -- probably guided by MPP and his team, who have most recently examined them:
Recent excavations and geophysical surveys have suggested the possible importance of geological features called periglacial stripes. They run parallel to the banks of the avenue and across the site of Stonehenge and align in places on the solstice axis. It is possible that these geological stripes may have been visible on the ground in early prehistory and could have led prehistoric people to believe that this was a special place.
Outline of the main differences between the 1st edition of the
English Heritage Stonehenge guidebook (2005, reprinted 2007)
and the 2nd Edition (2011) (download as PDF)
v) The possibility that Stonehenge's location was chosen as a result of the
coincidental alignment with the solstice axis of natural landscape features
(periglacial stripes underlying the Avenue) coupled with the occurrence of a natural
sarsen (the Heel Stone) at the end of that alignment.
A new paragraph has been added discussing the discovery of the existence of
natural Ice Age gullies parallel to the Avenue, and the possibility that the Heel
Stone is a rare local sarsen found near where it now stands, both features
providing a coincidental alignment on the solstices. It is suggested that this may
have provided the impetus for the building work that followed.
Added mention of the natural "visible stripes" that are Ice Age landscape
features in the chalk parallel to the Avenue along the straight section leading up to
the monument. Changed emphasis in discussing the solstice axis from "this cannot
be a coincidence" to "this alignment is deliberate".
If the evidence is reliable that these stripes run parallel with the first part of the Avenue (shown in both of the illustrations above) and even run through or beneath the Stonehenge earthworks, then that clearly suggests a great age for the features. But we don't really know how extensive they are -- maybe somebody who knows the evidence on the ground can enlighten us on that. If you look very carefully at this illustration you can see a faint line outside the Avenue edge which is interpreted as one of the "periglacial stripes."
What we need here is a detailed topographic survey, but my impression is that these stripes (like the Avenue) point towards the midsummer solstice or sunrise position on the horizon (have I got that right?) but that they do NOT run down the maximum slope inclination towards Stonehenge Bottom. If there is one thing we do know about periglacial stripes it is this: they always run down the maximum inclination of the slope. I have seen a lot of such stripes in my time, in Antarctica, Greenland and Iceland, and I do not recall a single one that was aligned diagonally down a slope.
In the absence of a detailed survey all I can do is speculate about this -- and to say that if these stripes really are periglacial in origin, they should be running from Stonehenge down towards the road junction we can see on the LIDAR image.
Far be it from me to suggest that something perceived as "natural" in origin should now be re-classified as "probably man-made" -- but that is exactly what I am doing!!