This tomb is classified as a portal tomb in the Carlow Inventory and on first sight you have to agree. A large capstone rests on two projecting portal stones with a full height doorstone in between - one wall of the chamber lies prostrate below the capstone.
However, closer inspection raises several issues. The portal stones are very low, just 1.2m, and the chamber would have been the same height. In front of the 'portal' there are definite signs of a courtyard and bits of the kerb . Walking to the rear of the tomb there are several slabs set across the line if the tomb in line with the chamber - perhaps indicating a gallery?
To me this just seems like one big hodge-podge of styles and really should be investigated properly. I'm sure that it would provide more questions than it answers though.
Portal tombs are what most people wrongly refer to as dolmens. They are, to me at least, the most strikingly designed of the megalithic tombs. They are called portal tombs because they have two large upright stones, usually very well matched, in front of the chamber that seem to form a doorway.
Resting upon the portal stones and the chamber a large capstone rests (sometimes there are two capstones - see Knockeen (County Waterford)), usually at an angle of around 22 degrees from the horizontal. Although these were originally incorporated into one end of a long cairn there are none left in this state today, although traces of the cairn can sometimes be seen upon the ground. The portal stones can be up to 3.5m tall, which combined with a thick capstone can produce an imposing monument over 5m tall. Capstones can reach in excess of 70 tonnes, with that of Browne's Hill (County Carlow) being estimated at over 120 tonnes.
Often betwen the portal stones there is a door slab, blocking the width of the entrance, but not always the full height. Door slabs are either half height, three quarter height or full height, describing the amount of the portal that they obstruct. All portal tombs would have had door slab, but this has often been removed to facilitate entry into the chamber.
Quite rarely the portal stones are the same height as the chamber and the characteristic slope of the capstone is created by the profile of the capstone (see Glendruid (County Dublin)).
A kerb is a ring of stones placed around the perimeter of a burial mound or cairn. It basically serves the purpose of a retaining wall to keep the cairn or earth in place. Kerbs are usually associated with passage tombs, but do occur on court tombs and wedge tombs too.
Sometimes on passage tombs the stones can bear decoration, such as at Newgrange (County Meath).
Due to the road arrangement in Borris I will give a indirect route here. From the west end of Borris take the R705 north for 2.5km and turn right. Continue and go over two crossroads. Turn right along the second farm track. Park at the sharp bend in this track. The tomb is 200m into the trees in a direct line with the track you have just driven down, but you can't really go straight to it. Head to the right and walk along the wall and keep looking into the trees. I wish you the best of luck, because I walked right past it and only found it on the way back by seeing the white Fogra sign.
This is an explanation of (and a bit of a disclaimer for) the coordinates I provide.
Where a GPS figure is given this is the master for all other coordinates. According to my Garmin these are quite accurate.
Where there is no GPS figure the 6 figure grid reference is master for the others. This may not be very accurate as it could have come from the OS maps and could have been read by eye. Consequently, all other cordinates are going to have inaccuracies.
The calculation of Longitude and Latitude uses an algorithm that is not 100% accurate. The long/lat figures are used as a basis for calculating the UTM & ITM coordinates. Consequently, UTM & ITM coordinates are slightly out.
UTM is a global coordinate system - Universal Transverse Mercator - that is at the core of the GPS system.
ITM is the new coordinate system - Irish Transverse Mercator - that is more accurate and more GPS friendly than the Irish Grid Reference system. This will be used on the next generation of Irish OS maps.