When we had the house built, we selected this area because it is rock. Our previous house had been built on dirt and so it shifted as the dirt contracted and expanded with changes in the weather. The idea was that at this location, we would have a solid foundation laid down on rock, and the house would be stable.
It appears this is not the case. As I dig down, I can see that there is dirt, then a layer of large rocks, then a small layer of dirt, then a layer of smaller flattish rocks (shelf rock someone called it), another thin layer of dirt and then bedrock. The foundation seems to be, at least at the edges, sitting on the large rocks, but there is still dirt and rock below that.
This continues from the corner of the house all along under the dining room and kitchen. I dug out all the rock and as much of the dirt as could reasonably be removed.
In place of the dirt, it seems that concrete is a better choice. So I used my standard wooden frames and poured concrete under the foundation along this section. I used 21 80-pound bags of Quik-crete to fill this section in.
All of this will be underground, once it is finished, so the appearance is not the main issue. We want to seal off the dirt and rock under the foundation, so that we don't have roots and water getting under there, making things unstable.
There is one more section, further up under the bay-window for the breakfast nook that I want to do also, but I have more excavation before I can do that.