Heavens' Henge

[jon]

Hi Boreades

It's unlikely that they were, especially in the case of Feddau and Eryr: It happens by chance. It's possible that the two chalk hills (Milk and Tan) had their summits modified but I've never been there so don't know if they have any signatures of this sort of thing

[hvered]

The idea that the two hills are of equal height by coincidence rather than by design doesn't really have much purchase. It should be understood by now that the whole area around Milk and Tan hills is man-modelled: it's the Wansdyke...a feature that stretches from Savernake Forest to the east of Avebury as far as the Dundry Down ridge, north-west of the Severn Estuary.

The TME view is the Wansdyke, like other dykes and grim's ditches on long-distance routes such as the Ridgeway, wasn't intended to prevent Anglo-Saxons, or whoever's supposed to be marauding, but a barrier to stop animals and drovers leaving the right track. Southern England may not have been the centre of all things megalithic but since it's a good place to start looking at landscape interventions since chalk seems to be the most malleable of rocks.

[jon]

The idea that the two hills are of equal height by coincidence rather than by design doesn't really have much purchase.

I think I agree with that Hatty. However, it's unlikely that the Preseli pair of peaks would be man-made: The rock type would leave a signature that doesn't appear to be there. When you take into account that the two sets of hills appear to be linked in the minds of megalithic builders (Stonehenge's bluestones came from Preseli), the probability decreases even further.

[Boreades]

Stonehenge's bluestones came from Preseli?

I thought that had been nailed as a myth.

[hvered]

How would anyone tell what was or wasn't 'natural' in a mining area such as the Preseli hills? It isn't always possible to tell where human activity has altered a landscape because unnatural can very soon become natural, particularly with artificial or modified hills I'd have thought. Carn Menyn is not in the least natural surely?

Location is an important aspect, navigationally speaking. Lundy is the critical bit to my mind, it's due west of Stonehenge as someone, Robin Heath, I think, has already noted, and Carn Menyn is due north of Lundy. And due north of Carn Menyn, at the northern end of Cardigan Bay, is Cardigan Island which appears to be a former causewayed island and still frequented by our beloved cormorants.




(Landscape intervention is often a question of period, no-one has a problem with, say, the Wansdyke or Offa's Dyke because they're assumed to be post Bronze Age, i.e. post-antler picks. Silbury is a bit of an anomaly, apparently!).

[jon]

"I thought that had been nailed as a myth."

Hi Boreades. Apparently not. The bluestones are a type found only in Preseli. The only question is whether or not they were quarried and brought to Stonehenge: The other possibility is that glaciers carried them in one of the ice ages.

There's some sort of archaeological activity going on under Prof Parker Pearson's banner to establish whether or not a neolithic quarry exists at a place called Rhos-y-Felin.

Rhos-y-Felin is just north of Feddau and Eryr and along the same route that leads down to the coast (the route starts at Eryr, then to Feddau, then down to Carn Ceodog and on north to a place called Castell Mawr (near Rhos-y-Felin). I understand that there is also some investigation into a nearby neolithic site that may once have held the bluestones before they got transported to Stonehenge. There are several candidates for this (nobody's telling), but if that place turns out to be Castell Mawr, we're pretty much in with a slam dunk (Castell Mawr is the one in the area that has some geocentric features)

[jon]

"How would anyone tell what was or wasn't 'natural' in a mining area such as the Preseli hills? "

The two peaks are Foels Eryr and Feddau. I doubt these would prove to be man-made but it would be easy to find out (one of the peaks should bear marks of that). It's unlikely in my opinion because we know that the Neolithic people built cairns at the top of the two summits. These are definitely unnatural and the cairn on the (slightly) lower peak is larger than the other: So if the people were trying to make them the same height, then the cairns would have done that job.

However, if the sequence is that the world's 'roundness' was discovered by accident (in Wales), then these two peaks are ideally situated for that and likely to be natural (apart from the cairns).

If the Neolithic people then carried a part of that place (of first discovery) to Stonehenge, they may well have modified the landscape at Tan Hill and Milk Hill to show what was discovered in Wales.

We have Ceasar's note about the druids claiming to know the size of the world and so on: These arrangements seem to back up their claims about that process of discovery?

[Boreades]

OK, I think I might have figured out how we could make the peaks the same height. It doesn't matter whether the peaks are aligned exactly east-west, we're just working on the days when the direction of sunrise and sunset are in the same direction as the line between the peaks.

1) From the peak furthest from sunrise, measure the apparent declination of the rising sun below/behind the peak nearer to the sun.
2) Repeat with sunset, and the apparent declination of the setting sun below/behind the peak nearer to the sun.
3) Compare the declinations.
4) Adjust the height of one peak by adding or removing material on the hilltop.

Repeat the cycle until the declinations are equal, or as equal as you want them to be.

Seemples. All it takes is time, patience, and careful observation and measuring.

[jon]

OK, I think I might have figured out how we could make the peaks the same height. It doesn't matter whether the peaks are aligned exactly east-west, we're just working on the days when the direction of sunrise and sunset are in the same direction as the line between the peaks.

Aha.. afraid it does: The only time that sunset and sunrise are in opposing directions is at equinox: The peaks need to be roughly east-west (as in the case of Feddau-Eryr) or they need to be wide enough so that it can be done slightly off equinox (as in the case of Tan-Milk)

If you tried to follow your procedure at Feddau-Eryr (Preseli), then you would get an error: The reason for this is that the lower sections north of the Cambrian mountain range, about 60km away at about +300m, raises the line of sight. If they had tried to alter the Preseli range using that method, Feddau would be 5-8 metres taller. Another reason to suppose that Feddau-Eryr might be natural?

However, it might work at the Tan-Milk hills. Hatty's only just told me about that so I haven't checked it.

[jon]

But have a look in the book: You'll find a water-level method described in the section that deals with the size of the world: There's not much to this as all it needs is a hollowed-out log and could easily be made to be very accurate. Today's equipment (theodolites and levels) use exactly the same principle.

From Tan Hill to Milk is about 2.5 km. From using similar equipment myself, I know that you can get an accuracy of about 2:10000 using the eye (ie no optics). Therefore you would expect a maximum error of +/- 500mm. For this max error, the errors all have to be cumulative and this rarely happens when you're doing a survey, so in practice you would expect an error of only about 150mm or so if a water-based levelling system had been used.