In reply to philhilo:
The quick answer is the wrong answer. . The mud was there, they were never preserved into the rock record. One of the reasons is lateral accretion and avulsion of rivers (meanders meandering, and then the river jumps to a new location during a flood), combined with a slowly subsiding basin (subsidence is important to preserve the sediments). The slow subsidence rate means that the river migrates and jumps many times at the same level, meaning that over-bank muds associated with with the flood plains are erroded and lost, and are replaced with sands sand bars (both within and at the edge of the channel). If that happens enough, you are just left with sand. Mam tor, as you mention is based with shale, but that's a different mechanism which caused the transition from shale at the base of the hill, into the Mam Tor grits (that was infilling of the basin by turbidites), and shouldn't be compared with the fell sandstone (deposited by rivers): they are two different environments.
OK, for igneous rocks generic questions such as "why are these crystals here coarse, and over there they are tiny", "why is granite light coloured, and gabbro/basalt dark coloured?", "why do igneous rocks tend to form big blocky outcrops", or "what can the type of igneous rock tell me about the history of the area?" would be good universal questions.
For metamorphic rocks, questions like "why are these rocks shiney!?!" or "why are these rocks folded" or "why have these rocks got layers and melted blebs in them?" or "what causes the sheety layering in slate, and why" would be good to ask.
These generic questions apply universally to most igneous/metamorphic/sedimentary outcrops across the world, as the processes governing the formation of the rocks are largely universal.
Oh, and questions for limestone: "when will the weather improve, so i can go back to climbing on the grit?" :-D