I found this post from Rajqawee, I put the link back because it's super interesting.
I was able to find my garden ... extract:
"Medium to gentle slopes of the West Lyonnais slopes, with silty sands and clay sands from gneisses, mainly meadows.
Dominant soil type: Alocrisols (100%) "
"Alocrisols are moderately thick to thick (more than 35 cm thick) acidic to very acidic soils, developed from sandstone alterites, shales or crystalline rocks, which are most often observed in forests or natural vegetation. Alocrisols are rich in exchangeable aluminum, potentially assimilable and harmful for plant nutrition. "
Good no luck for aluminum
I am surprised by the acidity because being on a rock quarry I thought the soil was rather limestone. I doubt even ...