GEOLOGY 



nodular knobs or in anastomosing veins or ribs within the rock, thus 

 giving it a strange and unique appearance. Where this segregation 

 has taken place the sandstone is generally bleached, so that on a weathered 

 surface the knobs and ribs stand out in white upon the yellow back- 

 ground. There are no fossils of any kind in the Yellow Sands deposit, 

 and its place as a true member of the Permian system, which has more 

 than once in time past been disputed, depends more upon the uncon- 

 formity between it and the upturned denuded edges of the Carboniferous 

 upon which it rests, and upon its complete (though not always well dis- 

 played) conformity with the overlying fossil-bearing, and therefore 

 proven, Permian Marl Slate. It may be added that the unconformity 

 referred to is shown not only by the denudation of the coal-bearing 

 rocks before the deposition of the sands, but also by the fact that most 

 of the dislocations affecting the Coal Measures stop short at and do not 

 affect the Yellow Sands. These dislocations are thus pre-Permian faults. 

 A few other faults affect both systems and are therefore post-Permian, 

 though some of these (whose vertical throw or displacement is less in 

 the Permian than in the Carboniferous rocks) are both pre- and post- 

 Permian, an interesting fact proved in several cases in recent years. 

 The denuded floor upon which the sands lie is irregularly undulating, 

 and the sands fill up the hollows and are there thickest — up to loofeet 

 or thereabouts as a maximum — becoming thin or being absent altogether 

 where the floor rises into diminutive hills. It is in the north and east 

 of the Permian area that the sands are most fully developed. In the 

 south and west they are either thin or wanting. 



So loosely coherent a deposit is necessarily a first rate water-bearing 

 stratum, and we find accordingly that the Yellow Sands play an im- 

 portant and twofold part in that capacity — a beneficent part so far as 

 water supply is concerned, though the water from this horizon is gener- 

 ally exceedingly hard, and sometimes, in the neighbourhood of the coast, 

 to a certain extent brackish — a highly inconvenient and occasionally 

 dangerous part from the mining point of view, since shaft sinking 

 through the sands where they are full of water is always attended with 

 great expense and many difficulties, and has more than once given rise 

 to floodings which it has taxed the resources of engineering to the 

 utmost to cope with successfully. 



The outcrop of the Yellow Sands is from the nature of the case 

 a narrow and an interrupted one, but where they are thick — as at 

 Houghton-le-Spring, Newbottle, Ferryhill, Claxheugh, etc. — good 

 sections can be examined, though none quite so good as those at Culler- 

 coats and Tynemouth in the neighbouring county. 



The present writer has elsewhere given quite recently a very full 

 account of this member of the Durham Permian from which the fol- 

 lowing theoretical conclusions, agreeing in the main with the views of 

 the late Mr. Richard Howse, may be quoted : — 



The history of the beginnings of the Permian system in Northumberland and 

 Durham, such as it can be gathered from the facts already stated and from the details 



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