Complex sentence: This bears an Ordnance Survey triangulation column beside a massive cairn, not now in the best of repair, but unmistakable from any distance, still six feet high and much greater in diameter.
Split into simpler sentences: This bears an Ordnance Survey triangulation column beside a massive cairn. This is not now in the best of repair, but is unmistakable from any distance, still six feet high and much greater in diameter.