The bloomin' rain lasted until an hour before dusk today, so no chance of getting to the plot. Been a dry January, so no complaints. Gave me time to think about all that gravel which is left over in the hand riddle. For every spadeful, (and a spadeful = a hand riddle-full), there's enough gravel to fill a half-pint glass, or thereabouts. Was it always there in the soil? I did a bit of research as the drizzle fell from a pale grey sky.
Allotment research is a relief from what I was doing for "real" academic research for the doctorate, in that it's fine to yield to a temptation to wander off-topic. On one such detour, I learned that it is opined that adding sand to clay is a really counterproductive thing to do, and will result in concrete.
I also learned from the RHS the definition of "heavy clay"; (to summarize, if you can roll it into a ball, thence to a sausage, and, after giving it a rub, if it's shiny, that's heavy clay - no, really.)
Back to the gravel. Several gardening advice sites suggest it as a means of breaking up heavy clay. This yin, for example. So I'm going to theorise that at some time in the past, perhaps when the ground was agricultural land, gravel was dug or ploughed in to the then clay topsoil to improve it. And it has worked well enough - I mean, it's garden-able. The heavy - RHS shiny-sausage - clay in the subsoil would not be.
Time has passed. There have been 100 growing seasons, with organic matter being added every year. Even when it was derelict, annual weeds grow and die and add to the ground. In recent decades, all of those currants and berry bushes, the cherry and ash trees, and nettles, left a lot of leaf mould. The paths I discovered were under 8-10ins of earth, so the beds must have gotten at least that much added to them.
The ground is clay, but there's a lot of organic matter in it now, as well as grit. The gravel has done its job, and can now do new ones: forming a hardcore base for the shed, and filling-in drainage ditches. It's my job this year to relocate all of these stony little labourers to their new places of work.