Slioch - Torridonian sandstone overlying Lewisian gneiss basement.
These are old rocks. In fact the shallow "valley" that you can see under the mountain so to speak, is an ancient landform that was subsequently filled with the sediment now forming the mountain and re-exposed. Uplift and erosion.
Mind bending stuff. That valley I can walk in was originally a valley millions of years ago; buried then re-exposed again.
The area I visited, and shown below, is at the bottom right of the picture
Dark hornblende gneiss of igneous origin.
Well I must go - think I'll take a break and start work after lunch and keep going till tea time. You can tell I am keen, it is like starting to study for exams. Only I'm getting too old for it these days. I need my weekend to recover and re-connect with who I am.