|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
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 =
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.
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.
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
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
• The amphibians left the seas in great numbers to colonise the
• 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.