Good luck on finishing your project!

Based on your pictures, it looks like it could be un-compacted clay. However, "looking" is the worst way to examine the material.

Clay is not just the next smaller size of particles below silt. It is actually composed of different minerals compared to silt derived from a parent rock of sandstone or limestone. True clays will develop "plasticity" when wet.

The best test is to get your material damp and then make a ball or worm out of the material by rolling it in your hand. If you can make a ball that persists, then you are dealing with clay.