The Sarn extending westward from Wallog divides into four - Sarn Wallog, Sarn Gynflein, Gynfelin Patches and Outer Patch. The water depths shown on this historic chart are 1-1 3/4 fathoms. Admiralty Sailing Directions dating to 1870 describe the elements making up to the whole - 'It begins as a narrow tongue of shingle and pebbles intermixed with large stones named Sarn Wallog, which stretches out seaward in a NW by W 1/2 W direction, and drying at spring tides for the distance of half a mile, but is entirely covered throughout its whole extent when the tide has risen from 6 to 8 feet. For the next 2 miles it assumes the name of the Sarn Gynfelin, and further out as the Gynfelin patches to the disatnce of 6 miles, when it suddenly terminates. A conical buoy, with black and white rings is moored on about 4 1/2 fathoms outside the danger...'

Sources include:
Admiralty, 1870, Sailing Directions for the West Coast of England from Milford Haven to the Mull of Galloway including the Isle of Man, pg40-41
Historic Admiralty Chart 1411_A5, RCAHMW digital collections sourced from the UK Hydrographic Office and first published in 1842

Maritime Officer, RCAHMW, August 2014.