Just had this reply from Steve Hartgroves, Principal Archaeologist
Cornwall Historic Environment Information Team
"The circular feature on the map has been surveyed and examined by the OS archaeological surveyors; they were unable to come up with a convincing interpretation.
The SMR says this:
PRN 1782: A roughly circular enclosure lying at the bottom of a gentle SE slope immediately above an area of marsh was located and surveyed by the OS in 1973 and surveyed from the air and on the ground by the RCHM in the 1980s. The enclosure measures 35m in diameter overall and consists of a turf bank up to 12.0m wide, and nowhere more than 0.7m high with a few exposed stones. There is a depression in the centre, but no trace of an entrance, and no sign of any round houses in the interior. In 1973 the OS recorded that its origin and purpose were 'obscure', but added that it may possibly be a small round. In 1984 Quinnell's view was that it was not a small round as previously suggested, but possibly a natural feature. This seems unlikely however; excavation may be needed to properly identify the function and date of the feature.
I don't suppose this is much help...it isn't likely to be a round in this location; could it be some kind of animal pound?"
I am not convinced, it aint natural that much I know!
Letter Moor is a small area of open moorland just to the south of Colliford Reservoir and north of St Neot. On the OS map a couple of cairns are marked plus a tumulus just to the south in a field. Slap bang in the middle there is marked on the recent OS Explorer maps a dotted circle, i was curious as to what this was so took a walk.
The whole area is made up of very gently slopeing moorland with gorse bushes here and there. There are a few lumps of granite poking up through the soil, I did line up five with a large stone at the southern end but decided I was imagining things...
I wandered around trying to see what the round object on the map could be, there was no obvious feature. Then I turned round to look at where I had come from and spotted it.
Lying on the gentle hillside and facing south east was a low earth circle with a depression in the middle. The circle was about 75ft across from bank to bank. There was no sign of stone in the low banks and the centre was very smooth all round.
I have no idea at the moment what this feature is but will look into it. It may be a cairn or tumulus but there is no sign of the earth or rock that must have made up the inside.
One other inteeresting feature is the fact that looking east from here I believe the sun would rise over Brown Gelly on Midsummer day whilst all the other high points of the eastern moor are equal distance in a row moving south