Vestiges of mining

I have often wondered what these two constructions are.  I think they may have been part of a furnace for smelting iron ore. There are many odd tunnels and old workings around the village.This morning I finished making the bread and had thought to go into town to call in at the tax office but found the answer to my question online. I applaud those admin monitored Facebook groups that provide useful information and discussion forums to answer obscure questions. I struggled on a French government website to upload details of the composition of the church Association (its governing body). It took a long time compressing, combining and loading documents but I got there in the end. Making more squash soup proved much easier!