Swaledale Geology Introduction

Swaledale Geology

The Geology of Swaledale and Arkengarthdale

Welcome to the SWAAG Geology pages. It is designed for people who want to “go and see” and have an explanation of what they are looking at. Each section will be introduced with a photograph and an overlay of what can be seen. The overlay will easily locate features on the photograph and there is a glossary of the terms used in each photograph and a short account of the geology featured. Each photograph has a grid reference linked to the Land Ranger O.S. maps e.g. OL30. There is also a simplified compass bearing to show the direction of the camera view and a location title.

The present is the key to the past so the starting point is to answer the question “Where could we find a present day Swaledale?” The answer is the Gulf of Mexico. Here we have the tropical seas of the Caribbean and a huge delta of the Mississippi encroaching from the north.

If you live in the Dales or just visit from time to time, you must have been impressed by the rugged grandeur of the Dales. It has always staggered me that all the rocks of the Dales were formed either in the sea or coastal swamps. This was during the Carboniferous Period which lasted some 70 million years (carbo = coal).

Imagine a post box full of letters posted over a period of time. If the post box is not opened for a long period of time (even longer than the Dales postal service) then the letters and messages begin to deteriorate. The letters at the bottom of the box (the oldest) are hardest to read. Rocks are just like the letters in that they carry messages from the past. The older the message the harder it is to read. The oldest rocks in Swaledale and Arkengarthdale are in the valley floors. The youngest rocks are seen on the higher levels as revealed on Fremington Edge and above. The oldest and youngest rock of the Carboniferous are not found in Swaledale, but a big slice of the middle is found.

Fremington Edge

Three main rocks are found in the Dales, and also in most of the neighbouring Dales. These are limestone, shale and sandstone. The miners of the past called these rocks by different names such as flag for limestone, especially if it was fissile – it splits easily. Shale was called plate and sandstones were called grits. The vast majority of sandstones in the Dales are not coarse enough to be classified as grits.

There are other rocks of some economic importance. These are lead, zinc, copper, barites and silver. They are all linked to previous emplacement of granites into the basement of the Pennines and their subsequent erosion. Many of the sedimentary rocks also had an economic role in the history of the dales. Limestone was burnt and turned into quicklime for improving the soil.

The Carboniferous must have been one of the most amazing geological periods. Consider the following statements:
• The world was spinning far faster than today so days were shorter but more in number – about 400 days in a year.
• The moon was much closer than today so tidal ranges would have been greater.
• The amphibians left the seas in great numbers to colonise the coastal environments.
• The primitive trees of the previous period, the Devonian, began to evolve and cover the land.
• The trees changed our atmosphere from one rich in carbon dioxide to one rich in oxygen. The oxygen excess caused gigantism in groups of creatures like the insects.
• All of this happened as Earth’s one continent called Pangaea, drifted across the equator.

The evolution of the Yorkshire Dales raises many questions. Some of the most fundamental questions are answered through geology and the study of rocks. Perhaps it’s time to take some of the mail out of the letterbox and see what we can discover about our amazing Dales and their evolution.

Use the Geology Menu at the top of the page to explore the geology section as it develops