Ribblehead, Dent and Garsdale

Out from Ribblehead Station, Whernside is up ahead. Around the Ribblehead viaduct the limestone is coated in a thick layer of glacial till, foundations for the viaduct were sunk down through 8m of this to reach bedrock. Drumlins indicate the ice moved southwest across the high ground along the western side of Ingleborough.

Sink holes at Ribbleshead viaduct – Anthony Glossop

From the viaduct, sink holes are visible. These are formed where ground water has dissolved the thick limestone. Many of the becks flowing off Blea Moor and Whernside disappear underground into this cave system. In the valley to the southwest of the viaduct, the River Doe rises, only to disappear underground again after a few hundred metres.

The line turns north and runs between Whernside and Blea Moor. Under the steep east face of Whernside are ridges of sandstone debris, the sandstone can be traced to outcrops further up the hill. The ridges are not in the right orientation to have been deposited by ice and the most likely explanation is they may have been formed by ‘gill bracks’ – snow avalanches which carry debris down hill. A letter from a Thomas Thistlethwaite of Habourgill to his brother and sister in Asygarth, dated 28th January, 1752 gives an account of farm buildings being destroyed by a gill brack and several people killed. The letter is reproduced in ‘The Geology of the country around Ingleborough’ (full reference given in references), published in 1890. The author notes that in 1890 no one living remembers sufficient snow in the Dales to cause avalanches. However, it is interesting to note that 1752 is close to the peak of the Little Ice Age (a time of unusually cold weather that lasted several hundred years and ended in the mid nineteenth century).

Horizontal limestone beds near Ribblehead viaduct – Anthony Glossop

Blea Moor Tunnel is cut through Carboniferous Limestone. The fossils found in these beds are typical of the warm, shallow, tropical seas in which the limestones were deposited and included Fenestella (similar to corals and sponges), bivalves (modern day examples include cockles, molluscs and oysters), corals and giant brachiopods. The line carries on through the same limestones from the tunnel to Dent Station.

Past Dent Station is Risehill Tunnel, in the debris left behind from building the tunnel are the fossils of Lepidodendron and Calamites. Lepidodendron is a club-moss. Today’s club-mosses are small herbaceous plants which spread over the ground and grow short erect branches from their stems. The Lepidodendrons that grew in the Carboniferous had trunks which could grow up to 35m high and 1m round at the base. Calamites was a tree-like plant, which grew up to 20m high and is related to horsetails. Both these plant remains came from a sandstone layer within the Carboniferous Limestone Group, suggesting a period were the sea withdrew from the area and more swampy delta conditions prevailed.

• Introduction, Geological History and Economic Geology
• Settle, Horton and Ribblehead
• Ribblehead, Dent and Garsdale
• Garsdale, Kirkby Stephen and Appleby
• Appleby, Langwathby and Lazonby
• Lazonby, Armathwaite and Carlisle
• Geological Terms and References

						Tunnels were hand drilled at a rate of 40 minutes per foot.