If you walk regularly in the Dales, as I do, you are often asked “have you ever climbed the three peaks?” Quickly followed by “what was your time?”. My answer is “yes” and “five and half years!” I have ascended all three peaks on many occasions: Whernside (2,415ft/736m), Ingleborough (2,372ft/723m) and Pen-y-ghent (2,277ft/694m), but never all three in the same day.

Whether you ascend any of the three peaks, or alternatively circumnavigate them by bike or car, you cannot help noticing they have distinctive shapes, flat topped, with terraced sides. Have you ever wondered why?

It occurs due to the underlying rocks and geology and forces of erosion from wind, rain, and ice. Ask any geography GCSE student the names of the rocks forming the Yorkshire Dales and West Yorkshire, and they would hopefully answer Carboniferous Limestone (oldest and deepest, lying to the west), Millstone Grit (in the middle) and Coal (youngest and most superficial, and in the east). All were formed during the Carboniferous period (360 to 300 million years ago).

A hard cap of Millstone Grit forms the flat top of the three peaks, and Carboniferous Limestone (often referred to as Great Scar) forms the platform on which the three peaks sit. This however doesn’t explain the tiered slopes.

300 plus million years ago, Yorkshire straddled the Equator, slowly drifting northwards to its present position. Limestone was being formed in shallow tropical seas, and then the younger Millstone Grit in deltas and complex river systems. In the 20 million years between these two important rock layers being laid down, the climate and sea-level were constantly changing. Different rock layers or strata were being deposited in a cyclical fashion. Shallow seas were laying down limestone, estuarine marshes - shales and mudstones, tropical rainforests (consisting of ferns, horsetails, and clubmosses) - coal, and deltas - sandstones and grits. Some of these rock layers are hard, such as limestone, sandstone, and grits, while others much are softer, including shale, mudstone, and coal. The latter erode more easily and at a faster rate, which explains the terracing. Collectively these layers of rocks are known as the Yordale series, deriving the name from the old name for Wensleydale. Yordale was where the river Ure or Yor flowed.

Never again will the ascent of one of the three peaks on foot or a picnic on their lower slopes be the same. Don’t rush, take time to examine and enjoy the whole picture, and the millions of years of rock formation and erosion.