A HISTORY OF DURHAM 



many miles to the west in Westmorland and Cumberland, between the 

 regularly bedded Roman Fell Series (Lower Carboniferous, beneath the 

 Scar Limestone Series) and the denuded older Palaeozoic rocks, there is 

 here no trace. The Ordovician and Silurian rocks on which the Car- 

 boniferous were deposited stood out as islands during the earliest Car- 

 boniferous times, and pseudo-basal beach formations were formed at 

 several horizons at various stages in the gradual submergence and bury- 

 ing of the ancient sea-floor. It is some of these old shingle beaches 

 which have, naturally enough, been not unfrequently regarded as base- 

 ment beds. 



Neither is the series of flaggy sandstones and quartzose conglomer- 

 ates known on the Pennine escarpment as the Roman Fell Series 

 continued into Durham. This thick set of beds thins away very 

 rapidly to the east, and wedges out before reaching the western 

 boundaries of the county. 



From the lowest known Durham Carboniferous stratum to the Mill- 

 stone Grit division, the rocks exhibit the remarkable characters of the 

 Bernician Series. They consist of oft-repeated alternations of grits, 

 sandstones, shales, fire-clays and limestones, with a few (far fewer than 

 in Northumberland, though more than in Yorkshire) thin and gener- 

 ally inconstant coal seams of small commercial value. The nature of 

 the series is in fact intermediate between that of the Lower Carbon- 

 iferous rocks of Derbyshire and Yorkshire and that of the cor- 

 responding set of strata in Northumberland and Scotland. There are 

 here no huge thicknesses of limestone such as obtain in this stratigraphi- 

 cal division further south, thicknesses which there fully justify the term 

 ' Mountain Limestone ' so often applied to it, a term quite inapplicable 

 to the thin layers of calcareous rock which represent them in Durham. 

 On the other hand the number of limestone beds is rather smaller and 

 their individual thickness rather greater (not their total thickness) than 

 in Northumberland. Indeed the entire group so closely resembles that 

 upper portion of the Carboniferous Limestone Series which, as it is 

 represented in the Yorkshire dales, goes by the name of ' Yoredale 

 Rocks' that the Geological Survey have used that term to denote the 

 whole of the Lower Carboniferous strata of Durham beneath the Mill- 

 stone Grit. This is somewhat unfortunate, since only the upper portion 

 of these beds really corresponds to the typical Yoredales, the lower portion 

 representing the massive Scar limestones whicli form the base of Ingle- 

 borough, Pen-y-ghent, and the other great hills of the West Riding. 

 The thickness of the whole in Durham varies from about i,ioo to 

 1,250 feet, the scries thickening gradually towards the north and north- 

 west, until in some parts of Northumberland it attains the enormous 

 thickness of 8,000 feet or, in places, even more. It is to be noted that 

 with increased total thickness in the direction stated there coincides an 

 increase in number of l:)oth limestones and coals, the former thinner, as a 

 rule, than in Durham, but the hitter thicker and much more constant — 

 so much so indeed as, in N()rthuml)erland and in a still greater degree in 



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