144 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



volcanic rocks. Where best developed it has a zone of tuff at the 

 bottom, a central and much thicker zone of bedded basalts, and an 

 upper group of tuffs, on which the Coal Measures rest conformably. 

 A few vents, probably connected with this volcanic tract, are to be 

 seen at the surface between Fenwick and Ardrossan. But others 

 have been buried under the Carboniferous sedimentary rocks, and 

 have been discovered in the underground workings for coal and 

 ironstone. These mining operations have, indeed, revealed the 

 presence of far more volcanic material below ground than would be 

 surmised from what can be seen at the surface. Here and there 

 thin layers of tuff appear in brook-sections, indicating what might 

 be conjectured to have been trifling discharges of volcanic material. 

 But the prosecution of the ironstone-mining has proved that, at the 

 time when the seam of Black-band Ironstone of that district was 

 accumulated, the floor of the shallow sea or lagoon where this 

 deposition took place was dotted over with cones of tuff, in the 

 hollows between which the ferruginous and other sediments gathered 

 into layers. The seam is in one place thick and of good quality ; 

 yet only a short distance off it is found to be so mixed with fine 

 tuff as to be worthless, and even to die out altogether. In one pit- 

 shaft about a mile and a half to the south-west of Dairy, a thick- 

 ness of 115 fathoms of tuff was passed through, and in another 

 pit 90 fathoms of similar tuff were sunk into before the position of 

 the ironstone was reached by driving levels through the tuff into the 

 sedimentary strata outside of it. Only a short distance from these 

 thick piles of tuff, their place is entirely taken up by the ordinary 

 sedimentary strata of the district. The working-plans of the mines 

 show the tuff to occur in irregular patches and strips, between 

 which the ironstone is workable. From these data we perceive 

 that the shafts have in some cases been sunk directly upon the tops 

 of puys of tuff which were, in one case, nearly 700 feet, and in 

 another instance, 540 feet high.^ 



One of the most interesting developments of puys lies in that 

 little-known tract of country which stretches from the valleys 

 of the Teviot and Eule Water south-westwards across the high 

 moorland watershed and down Liddesdale. Through this district 

 a zone of bedded olivine-basalts and associated tuffs runs in 

 a broken band which, owing to numerous faults and extensive 

 denudation, covers now only a few scattered patches of the site over 

 which it once spread. The geological horizon of this zone lies in 

 1 Explanation of Sheet 22, Geol. Surv. Scotland (1872), p. 16. 



