No allotment today. I'm doing that much hard labour, I need to stay away every third day to recover, as I believe weight-lifters do. I used to ridicule folk who appeared to be addicted to the gym, but I understand them now - you can't beat that well-being sensation you get from the exercise-released endorphins.
The foundations consist of two courses of bricks, and a bottom layer of concrete. It goes right down into the subsoil, heavy orange clay. I'm surmising that Glasgow must have once been a glacial lake - according to Professor Wikipedia, clay is "associated with very low energy depositional environments such as large lakes and marine basins". All of the pebbles I've found would bear that out, there's a lot of quartz, smooth and round, what you'd find on the seashore.
Uncovering the foundations, and then digging down has left me with a trench which will extend across the width of the West bed, about 2 to 3ft deep, and 3ft wide. So I've inadvertently started to bastard-trench it. I wish I had some manure to hand. This is the shallowest top soil of the allotment that I've encountered so far - about a spit and half, most of the rest of it has been 2 or 3 spits. And this area is artificially raised by the presence of the foundations, so if the whole bed was level, there'd only be a half spit or so of top-soil.
So I'm going to take the level out of the subsoil, the clay. I'll barrow the clay to somewhere out of the way, and keep it covered so it doesn't dry out, and use it to line the pond. A proper clay-lined pond is a much more eco-friendly, logical and right-seeming idea in an allotment with heavy clay subsoil than plastic. And it's free, (apart from the prodigious amount of heavy dirty work that will need doing): that's proper allotmenteering.