of Limestones in High Teesdale. 261 



limestone, 20 or 30 feet high, stand (1876) close against sandstone 

 and shale, but when the margins of the limestone are examined by 

 hushing, etc., they show no vein, and they do not continue in nearly 

 straight lines as most veins do. Parts of the limestone stand up 

 like ruined towers on the floor of Blackway Hole hush, and it is said 

 they remain much as they were when originally found stickitig up in 

 a mass of famp. 



The famp in the Yad Moss level is mixed with irregular streaks 

 of a black earthy mineral, part of which is probably a black ore of 

 manganese. In the West Beck and Old Langdon hushes the famp 

 consists of nearly pure iron ochre, and it would no doubt have been 

 used for smelting if it had been in a more accessible locality. In 

 Weardale a famp of similar character has long been largely worked 

 for this purpose. The light yellow varieties of famp ai'e sometimes 

 used instead of whitewash, for painting over walls, etc. 



The limestones in Teesdale, which, next after the Great Limestone, 

 are most conspicuously famped, belong to the Melmerby Scar group 

 of limestones, in the neighbourhood of Silver Band Mine, Cronkley 

 Fell. These limestones and the Great ai'e generally rather pure 

 limestones (the Great usually contains about 95 per cent, of carbonate 

 of lime), so that the famp cannot be solely the residue of their 

 decomposition. The greater part of it must have been introduced 

 from without. It is most abundant where veins of ore are most 

 numerous, and it is probable that most of the famp material was 

 introduced by the same agent which filled so many of the neigh- 

 bouring veins with ironstone and other minerals. 



Where an ironstone vein passes through limestone, the width of 

 the vein is nearly always greater than in sandstone or shale, for the 

 limestone ' cheeks ' are converted into ironstone for a certain breadth 

 at the sides of the vein. The ironstone has not only grown in the 

 open fissure of the vein or fault, but has also replaced part of the 

 limestone. This is shown by the casts of corals, crinoids, etc., which 

 are found in the ironstone. In a similar way, also, where a quartz 

 vein passes through limestone, the limestone on the sides is partly 

 replaced by finely crystallized quartz. 



We suppose that the fissures made in the course of earth move- 

 ments formed channels for the circulation of water holding various 

 minerals in solution, and that this water not only deposited minerals 

 in the fissures, but also gradually dissolved part of the limestone it 

 passed through, and deposited other minerals in its place. The 

 replacement effected along the sides of the veins varies greatly in 

 extent, and it is probable that a replacement by carbonate of iron 

 was the first stage in the manufacture of famp. 



But why is the limestone more often dissolved away along the 

 outcrop than elsewhere ? It appears as if the action, which was 

 first started by water circulating along the veins, had been continued 

 and modified in recent times, since the present surface of the ground 

 was developed, and that this later action is perhaps still in progress. 



It is obvious that where a limestone was already partly dissolved 

 away near the outcrop, the ground above would be affected by local 



