Geology of County Durham
Coal Measures
### Coal Measures

Overlying the Yoredale Group rocks is a thick sequence of Coal Measures across which the [Durham Coalfield](/wiki/Durham_Coalfield "Durham Coalfield") developed. The sequence in County Durham is divided into Lower, Middle and Upper formations. Each of the three are dominated by mudstones but contain abundant sandstones and [coal seams](/wiki/Coal_seam "Coal seam"). [Ironstone](/wiki/Ironstone "Ironstone") bands occur in the lower part of the sequence. At least eleven [marine bands](/wiki/Marine_band_%28geology%29 "Marine band (geology)") (shelly mudstones in general) occur within the Coal Measures. Of these, the 'Quarterburn' marine band defines the base of the Lower Coal Measures Formation, the 'Harvey' marine band defines its junction with the overlying Middle Coal Measures Formation and the 'Down Hill' marine band defines the latter's junction with the Upper Coal Measures Formation. The Quarterburn, Harvey and Down Hill marine bands correlate with the standard *Subcrenatum*, *Vanderbeckei* and *Cambriense* marine bands of elsewhere. The top of the entire Coal Measures sequence is an erosion surface.Stone et al 2010 *British Regional Geology: Northern England* (5th edition) (Keyworth, Nottingham: British Geological Survey) p

* [Pennine Coal Measures Group](/wiki/Pennine_Coal_Measures_Group "Pennine Coal Measures Group")
	+ [Pennine Upper Coal Measures Formation](/wiki/Pennine_Upper_Coal_Measures_Formation "Pennine Upper Coal Measures Formation")
	+ [Pennine Middle Coal Measures Formation](/wiki/Pennine_Middle_Coal_Measures_Formation "Pennine Middle Coal Measures Formation") (Duckmantian)
	+ [Pennine Lower Coal Measures Formation](/wiki/Pennine_Lower_Coal_Measures_Formation "Pennine Lower Coal Measures Formation") (Langsettian)

Over the [Alston Block](/wiki/Alston_Block "Alston Block") the middle and upper Coal Measures are missing. Similarly in the [Stainmore Trough](/wiki/Stainmore_Trough "Stainmore Trough") on the [Yorkshire](/wiki/Yorkshire "Yorkshire") border, both the upper part of the Middle and the entire Upper Coal Measures are absent. The [rank](/wiki/Hilt%27s_Law "Hilt's Law") of coal increases in the west, a result of the heating of these strata by the Weardale Granite. Some such seams are semi\-[anthracites](/wiki/Anthracite "Anthracite"). Workings for coal date back centuries though the height of the industry was the nineteenth century. There are no deep pits remaining in the county though opencasting continues.

Various of the county's Coal Measures sandstones have been quarried for building stone, for example the Low Main Post sandstone in [Durham](/wiki/Durham%2C_England "Durham, England") which was used in the construction of the [city's cathedral](/wiki/Durham_Cathedral "Durham Cathedral").


Why does the rank of coal increase in the west?