GEOLOGY 



found in varying abundance in every one of the limestone beds 

 enumerated. 



The usual shale and sandstone interval is succeeded by 



No. 169. T^he Sixth or Sciir Limestone. — This must not be con- 

 founded with the previously described No. 217, which sometimes is 

 also known as the ' Scar Limestone,' the qualifying word ' Melmerby ' 

 being omitted. It is an important horizon in the lead measures, since 

 many of the richest ore- deposits have been found associated with it. 

 There are within it three thin bands of shale (locally ' famp ' in the 

 lead districts only) which separate the limestone into three posts or 

 courses. As lead veins of small faulting capacity traverse this bed, the 

 ore is apt to extend in great horizontal lateral masses along the ' famp ' 

 partings and to form those exceedingly valuable masses of ore known 

 amongst the lead-miners as ' flats.' Though only about 30 feet thick 

 this limestone has in many a mine yielded not only a thick vertical 

 main vein but a ' high,' a ' middle ' and a ' low ' flat of thick ore 

 of great value in the days before Free Trade. 



More shale and sandstone, and then 



No. 166. The Fifth or Five-Tard Limestone. — Notwithstanding its 

 name, this bed is only 7 or 8 feet thick, and is not very constant at 

 that. 



Shale and sandstone as before, then 



No. 162. The Fourth or Three- Yard Limestone. — True to its name 

 this bed is generally about 12 feet thick. 



Shale and sandstone, with usually a good deal of clay ironstone 

 (formerly worked before foreign iron ore was imported on a large scale) 

 associated with the shale, then 



No. 160. The Four-Fathom Limestone. — This bed again justifies its 

 name, being about 24 feet thick on an average. Although not restricted 

 to this horizon, yet the large Foraminifer Saccammina carteri occurs in 

 such special abundance in it that the limestone is often spoken of as the 

 ' Saccammina Limestone.' Long before the nature of the fossil was 

 recognized by the late Dr. H. B. Brady the miners and quarrymen knew 

 the band in the stone which is made up of the little spindle-shaped 

 tests as the ' spotted post,' though it must be added that they some- 

 times gave the same name to certain portions of other limestones with 

 ' spots ' — or sections — due to other fossils, especially corals of the genera 

 Lithostrotion and Syringopora transversely cut. The Four-Fathom and 

 the other limestones above it are among those which are most obvious 

 and 'feature-making' in the upper dales of the Tees and Wear. They 

 appear as long continuous short-grass covered zones running across the 

 country and contrasting strikingly with the ranker vegetation on the 

 shales and sandstones between them. Sheep congregate specially on 

 these deep green bands ; houses, where possible, are built on them, and 

 when the snow melts it is from them that it is first completely cleared — 

 a hint to house-builders and others that the conductivity for heat of a 

 rock is not an element to be neglected in selecting building sites. 



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