Geology
The underlying solid geology of the Rossendale fells is largely formed by the Lower Coal Measure comprising bedded sandstones, shales and mudstones. Rocks of the Millstone Grit series outcrop above the valley of the River Irwell and cap the hills. Musbury Tor is a perfect example of peneplanation leaving an almost isolated flat-topped hill where the harder Millstone Grit protects the softer underlying shales, leaving the distinctive sharp topography of edges and ledges characteristic of the uplands above the Irwell Valley.
The other small scale topographic variations such as the undulating hummocky landforms are generally due to the former workings and stone quarries.
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