Swaledale is one of the most northerly dales in the Yorkshire Dales National Park and one of the most remote, with a rich and varied geological history.
At the heart of Swaledale’s spectacular landscape are the Carboniferous age rocks, which lasted from around 360 to 300 million years ago. The Carboniferous, arguably more than any other geological time, is emblematic of the geology of northern England, and of Yorkshire in particular. The mineral resources present within Carboniferous strata were of paramount importance in the development of the Industrial Revolution in Britain and controlled the location and growth of many of our northern cities and towns.
The Carboniferous of Swaledale is dominated by the Yoredale Group creating a stepped landscape of flat-topped hills with steep slopes formed of limestone and sandstone. These are interspersed by broader more gentle slopes formed by the less resistant mudrocks. At the top of the Yoredale Group, the Main Limestone (or Great Limestone) is found in a prominent band and is responsible for several prominent scars and limestone features, such as the limestone cliffs on Cotterby Scar near Keld; Kisdon and Ivelet Scars above Muker and the high scar of Fremington Edge. The influence of limestone is visible in the vegetation type of the dale-sides, limestone supporting brighter green, species-rich grasslands in contrast with the coarser grasses on sandstones and shales.
The Millstone Grit lies on top of the Yoredale Group comprising a series of coarse sandstones with intervening shales and occasional coals. On the north side of the River Swale valley between Keld and Arkengarthdale, there is a concentration of east-west faults containing calcite, baryte, witherite, fluorite and galena (lead ore) and, in some places, deposits of zinc and copper ores. The horizontal gritstone strata, caps the moors to the north and south of the dale forming an extensive plateau of heather, cotton grass and peat.
Glacial deposits and landforms, a legacy of the last major glaciation, mantle the area and tell of past ice sheets and meltwater.
The area’s stunning situation and varied scenery make Swaledale a wonderful area to explore and discover the links between geology, landscape, biodiversity and industrial heritage.
Geological time is the extensive interval of time occupied by the geological history of the Earth. Many of the rocks in the landscape making up Swaledale are older than 300 million years old and this age can be difficult to grasp when human life expectancy is usually less than 100 years. Geologists when studying rocks, fossils and key events use a geological timescale that is a system of chronological dating that classifies the geological layers (strata) in time. The time scale was developed through the study and observation of layers of rock and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilised remains and imprints. The keepers of geological time are the International Commission on Stratigraphy (ICS) an international non-governmental body with the very humble mission of “setting global standards for the fundamental scale for expressing the history of the Earth”. The ICS produce an internationally agreed geological time chart that is updated yearly. It is this geological time chart that geologists use when assigning dates to rocks and strata, just like those in Swaledale from the Carboniferous geological time period.