Watford Observer reporter Martin Booth wonders if he may have stumbled, quite literally, on a piece of history by the Grand Union Canal at Croxley Green.

Martin explains: "Some weeks ago I was calmly cycling beside the Grand Union Canal, as I do every day when travelling to and from work, when I was violently flung from my trusty steed and came within a spoke of swimming with the fishes.

"After calmly dusting myself and my bike down and investigating tears to my shirt and trousers, I had a look at what caused me to crash. About 100 yards from Lock 79, the Common Moor lock, on the side of the canal with the new housing development, is an area of concrete which has a 20 foot-long gash in it.

"This is not the trail of blood from my embarrassing loss of equilibrium, but what looks like an old rut that used to provide passage for a wheel once upon a time. I know that Croxley Mill was near this site. Does anyone know if the cause of my crash is related to this, or is it something completely different?"

Martin has taken a photo of the curious obstacle can any reader advise him on what it might have been?

While discussing this puzzle, Martin and I pored over a 1903 map which shows a railway spur line running from the old Watford to Rickmansworth branch line to the Croxley Paper Mills.

We noted that the line branched a short distance after passing under Tolpits Lane in the Rickmansworth direction and debated what now stands in the spur line's path. Can anyone clarify exactly where the route was? Do any readers have any memories of working at the Croxley Paper Mills, any photographs of the buildings and employees or recollections of operations on the spur line?