GEOLOGY 



Scotland, to give the value of a workable coalfield to the area occupied 

 by the Carboniferous Limestone or Bernician Series. 



Although, as has been explained above, all the lower beds of this 

 important division are not to be seen cropping out at the surface in the 

 county, yet all have been proved within its boundaries by mining opera- 

 tions. Long before geologists had begun to survey the district scientifi- 

 cally the lead-miners had become familiar with every stratum between 

 the Millstone Grit and the floor of denuded Silurian and Ordovician 

 rocks. To each stratum a name had been given by them, and the 

 changing characters which they displayed from place to place had been 

 carefully observed and often recorded in the plans and sections connected 

 with the mines. It is to these early lead-miners, and more especially to 

 Mr. Westgarth Forster, who in 1817 gathered their observations and 

 his own in a complete and singularly able treatise, that we owe our first 

 knowledge of these strata. 1 About 120 well marked beds or sets of 

 beds are recognizable in the series, and have been measured over and over 

 again in countless shafts and levels. The best known and most char- 

 acteristic of these may now be enumerated, beginning with the lowest 

 and denoting them by the numbers used in Forster's classical section. Be- 

 fore proceeding, however, it will be well to state that special prominence 

 is given to the limestone beds, because, though by no means the thickest, 

 they are much the most constant and serve as datum lines of great value 

 in correlating the deposits present in one shaft or region with those found 

 in another. Besides it is in the limestone layers that the lead veins have 

 as a rule been found to be richest in ore. 



No. 2 1 7. The Melmerby Scar Limestone. This, the thickest lime- 

 stone in the county, on an average 132 feet thick, comes nowhere 

 within it to the surface. It has been proved in several mine-shafts 

 however. It is the nearest approach to the true ' Mountain Limestone' 

 type to be found in Durham, but being only known underground it 

 cannot form * mountains ' in any true sense. Miners frequently call this 

 mass of limestone * the Great Limestone,' but as that name is given more 

 generally to another much better known horizon considerably higher 

 up this practice should not be adopted. This thick limestone is not 

 continued as a separate bed into Northumberland, but is there repre- 

 sented by shales and sandstones, and even by a few thin seams of coal 

 with occasional thin bands of limestone only. 



After a small interval of shale and sandstone comes 



No. 214. Robinson's Lime. A limestone 20 or 21 feet thick. 



More shale and sandstone of no great thickness separates this from 



No. 208. The Smiddy Limestone. About 3 1 feet thick or a few 

 inches more at its maximum. 



Shale and sandstone again, then 



No. 204. T6e Tenth or Little Limestone. The latter name may, 

 as in the case above referred to, lead to some confusion, as another 



1 Treatitt of a Section oftht Strata from Nnofaitle-ufon-Tyne to the Mountain! t/Crou Fill Cumbir- 

 lanJ, by Wetgarth Forster. 



