This time of year they say spring travels at 1 mph during daylight hours starting in the south and moving north slowed only by altitude, which on maps is shown as contour lines .
The first Geodetic Levelling of England and Wales was done between 1840 and 1860 which is where this mark on an old sand stone building in Treflach originates from. It is 620 feet above sea level. There are few of these in country areas with most being in towns, but they disappear all the time due to erosion and redevelopment. They originate from an arbitrary benchmark 100 feet below St Johns Church in Liverpool. Due to tidal surges from the river and estuary anomalies in 1915 the Ordnance Datum Newlyn (ODN) at Newlyn on the South Coast of England was first used as the benchmark for mean sea level.
Even within the hills of Treflach, on lime or sand stone ridges with a southern aspect, spring can come early and autumn late.
thank you for explaining benchmarks Andrew. We enjoyed meeting you a few days ago, and admiring your Fresian bulls. I also enjoyed some other items in your blog – especially about the elms in the hedges. I wondered if I had identified them wrongly because I believed that they had all gone.