macausland wrote:I see that one of the very near islands is called 'sheep island'. Would that have anything to do with herding and driving animals?

Sheep island is almost inaccessible. Apart from the tidal races, there are steep cliffs and a reef to contend with, an ideal animal pen. Interestingly, the island also has a rock arch but it's facing north-west, the opposite side to the Sanda arch.

I think we can now make definitive judgements on these 'rock arches'. If these are natural products of natural processes we would expect them to crop up fairly regularly all over the wold. They do not. They are ridiculously concentrated in crypto-Megalithic places. It is reasonable to suppose therefore that, like Venus Pools and causewayed tidal islands (and in fact tidal island per se), these are to be regarded as Megalithically constructed unless, in any individual case, there are urgent reasons for concluding otherwise.

Of coure that now requires us to work out what rock arches are for and please no "They're Art" or "They're for ritual purposes". Megalithics are invariably practical people. Nor would the phrase "They're navigational marks" be acceptable unless some underpinning is provided.

According to the 'Natural Arch and Bridge Society' they do turn up all over the world, even in deserts.

http://www.naturalarches.org/gallery.htm

Would the existence of a coastal arch have an effect on the currents in the area?

Mick Harper wrote:I think we can now make definitive judgements on these 'rock arches'. If these are natural products of natural processes we would expect them to crop up fairly regularly all over the wold. They do not. They are ridiculously concentrated in crypto-Megalithic places. It is reasonable to suppose therefore that, like Venus Pools and causewayed tidal islands (and in fact tidal island per se), these are to be regarded as Megalithically constructed unless, in any individual case, there are urgent reasons for concluding otherwise.

Of coure that now requires us to work out what rock arches are for and please no "They're Art" or "They're for ritual purposes". Megalithics are invariably practical people. Nor would the phrase "They're navigational marks" be acceptable unless some underpinning is provided.

Err, timorous noise from the back....

I beg to differ. Yes for sure there are relationships here, but what came first? The megalithic Western Coast of Europe is also defined by extreme tidal ranges (in comparison to most other coasts). These tidal ranges, and the exposure to extremes of North Atlantic weather, have huge force over milllennia to reshape whatever coastline the tides and weather fall upon. Rock weathering is one natural consequence, hydraulic fracturing is a very powerful technique to undercut and cut through fissures and cracks in rocks. Hence the ridiculous concentration of rock arches and stacks in megalithic areas.

(rushes for cover before flamethrowers are lit)

http://www.youtube.com/watch?v=iT4SdLiZ3M8

http://www.youtube.com/watch?v=q55tSCFvZNU

Here's a couple of videos to whet or wet the appetite regarding sea arches.

The first is a climber off the coast of Donegal, the other is a paddle through by kyakers in the same area.

http://www.youtube.com/watch?v=aaX_R6WkoC8

Here's another seven

Megalithics are invariably practical people. Nor would the phrase "They're navigational marks" be acceptable unless some underpinning is provided.

An arch is reminiscent to my eye of the top end of an ankh. I wonder if arches enabled mariners to take bearings, from the landward side presumably, either for 'island-hopping' or long-distance purposes. Useful for direction finding even on sunless days?

http://www.bbc.co.uk/dna/mbhistory/html ... ad=6090118

The first comment on this site gives a description of the possible use of an ankh for direction finding.

Or perhaps it was used as a depth sounding weight attached to a line?

Ankhers aweigh?

According to the 'Natural Arch and Bridge Society' they do turn up all over the world, even in deserts.

Well, we must not jump to the conclusion that the desert ones are natural. If we found, say, that they all occurred in the Western United States, I would take that as highly suspicious. From the name of the society, I would not expect much help from this quarter.

I beg to differ. Yes for sure there are relationships here, but what came first? The megalithic Western Coast of Europe is also defined by extreme tidal ranges (in comparison to most other coasts).

This turns out not to be the case. Yes, some Megalithic sites eg Channel Islands, Mont St Michel, Bristol Channel, have large tidal ranges but other Megalithic sites (quite nearby) curiously do not. For instance, the most famous sea-arch of all, Durdle Dor, is down the coast from Poole Harbour which, I am assured, has a very small tidal range (not to mention four tides a day). Since presumably arches are a good indicator of the state of the tide -- and why is Durdle Dor always visibly an arch if there are thirty foot tides in its vicinity? -- then some correlative work is called for.

Actually, come to think of it, why do arches so often appear at exactly the right height? Shouldn't a whole bunch of them be too low (underwater) or too high (on land).

These tidal ranges, and the exposure to extremes of North Atlantic weather, have huge force over milllennia to reshape whatever coastline the tides and weather fall upon. Rock weathering is one natural consequence, hydraulic fracturing is a very powerful technique to undercut and cut through fissures and cracks in rocks. Hence the ridiculous concentration of rock arches and stacks in megalithic areas.

So, we have Boreades word for the fact that the extremes of North Atlantic weather confine themselves to places where sea-arches occur and the Megalithics decided to operate in areas where there are sea arches, despite these places being subject to the extremes of North Atlantic weather.

It is imperative, when mouthing orthodox explanatons, to apply a modicum of scepticism. Always remember that academics are rational (however stupid they are). Their explanations normally pass muster for at least the first few seconds of mature thought.