A HISTORY OF DURHAM 



workable seams are made up of numberless sandstones, shales, fireclays, 

 and thin worthless coals. Owing however to the extreme variation in 

 thickness of these strata — a variation which the continual splitting up 

 and reuniting of the coal seams necessarily implies — no good purpose 

 can be served in a brief synopsis like the present by going into numerical 

 details respecting them. Suffice it to say that the sandstones vary from 

 the coarsest grit to the finest grained sandstone, from massive building 

 stone and material suitable for grindstones to roofing flags, from dark 

 brown to every shade of yellow, grey and occasionally to pure white ; 

 that the shales, locally known as ' plate ' or ' metal,' vary also from 

 highly arenaceous clayey alternations (' grey beds ') to the finest laminated 

 unctuous bluish beds, and that they frequently contain concretionary 

 nodules and thin continuous bands of clay ironstone sufficiently rich in 

 carbonate of iron to pay handsomely for working in the old days ; and 

 that the underclays and other fireclays are usually excellent in quality as 

 material for refractory bricks or pottery. 



THE PERMIAN SYSTEM 



Overlying the denuded Coal Measures and some of the Lower Car- 

 boniferous rocks from close to the mouth of the Tyne near South Shields 

 to somewhere between the Hartlepools and the mouth of the Tees, and 

 therefore unconformable upon everything beneath them, come the Per- 

 mian Series of the north-eastern type, admirably displayed as regards its 

 thicker members in the coast section. It may be premised that these 

 north-eastern Permians are much more closely allied in aspect and 

 arrangement to the Permian or Dyas series of the continent than to the 

 much nearer representatives of that system in the north-west of England 

 on the opposite side of the Pennine range. 



The lowest of the Permian beds on this side of England are better 

 shown in Durham than elsewhere, but they are not visible along the 

 coast in Durham, though excellently exposed in the Cullercoats and 

 Tynemouth cliffs in neighbouring Northumberland. They can however 

 be studied in many fairly good sections inland, along the foot of the 

 Permian escarpment, and still more fully by means of the many borings 

 and sinkings which in the Permian area pierce through them in order 

 to reach the Coal Measures which lie immediately beneath. These 

 Permian basement deposits are known as the Yellow Sands. 



They are not universally present, even in the county of Durham, 

 but where present they consist of highly false-bedded sandstones ranging 

 in colour from the bright yellow which gives them their name to red 

 on the one hand and (rarely) dark grey on the other. The grains of 

 sand of which the rock is chiefly made up are of moderate size or 

 quite coarse, hut usually rounded after the manner of desert sand and 

 very unlike the angular unworn grains of ordinary grits. More often 

 than tu)t tliese grains of sand are so incoherent as to crumble between 

 the fingers, but sometimes they are cemented more or less firmly by 

 carbonate of lime. Carbonate of lime has also frequently segregated in 



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