326 ALTERNATIONS OF BEDDED TRAP AND LOWER SILURIAN ROCKS. 



a. Coarse slaty felspar rock, slightly porphyritic and amygdaloidal, containing elongated concretions of green earth. 

 It is regularly stratified in beds of 3 to 4 feet thick, and forms the mass of the hill, rising into the higher ground. 



feet, inch, 



% Finely laminated greenish-grey sandy flagstone, apparently hardened near the trap 50 



c. Fine-grained granular felspar and courses of clay-stone, some of which are used as oven stone 30 



d. Altered flags, having a conchoidal fracture, in parts almost Lydian-stone, with crystals of iron pyrites 10 



e. Grey felspar rock, the lamina} of deposit marked by ferruginous streaks probably due to the decomposition"! 



of some other mineral. A thin transverse vein of quartz with some lead (ranging south-easterly) induced I ^ 

 some of the inhabitants to drive a gallery across the beds, an effort which terminated as fruitlessly as all j 



the other mining speculations in these hills . J 



/. Black shivery shale, containing a few concretions of argillaceous limestone, with veins of calc spar. One"! 

 of these which fell under my notice was a septarium, two to three feet in diameter, containing many im- j- 10 



pressions of Graptolites 1 - J 



(This band of black shale has been recently excavated to a considerable distance on the strike of the beds by 

 the same individuals who have sought for lead ore. In this case their object was coal, necessarily a great deside- 

 ratum in a district so far removed from any coal-measures. The ignorance of the speculators in this case was 

 surely never parallelled, their gallery having been driven for the whole distance in the very same stratum of shale, 

 with an inclined wall of trap rock upon each side of it.) 



g. Hard, thick-bedded porphyritic felspar 4 



h. Flagstone with Asaphus Buchii ; indurated in contact with the trap ; much iron pyrites 20 



i. Grey porphyritic clay-stone 25 



j. Black schist, with some hard stone bands, in parts pyritous 100 



k. Slaty porphyritic felspar 5 



I. Black shale, with stone bands and concretions of argillaceous limestone 30 



m. Thin band of decomposed, granular felspar, weathering to a rusty colour and looking like a coarse oolite ... 3 

 n. Black pyritous schists, much contorted near the mouth of the gallery ... 40 



Total... 353 3 



Thus in 350 feet are exposed twelve bands of stratified trap, alternating with Silurian schists and 

 flagstones. 



The black shale decomposing into thin shivery fragments, has frequently induced the belief that it 

 was coal shale, and it has in consequence been repeatedly explored for coal. The same individuals 

 who foolishly excavated so far in the same black stratum in search of lead ore, had previously driven 

 a gallery to find coal 40 yards across these very inclined strata, the edges of which are exposed on 

 the sides of the adjoining gulley. Thus they actually drove through those very beds of which the 

 rivulet had already explained the true nature. It is needless to add, that when the work reached 

 one of the hard bands of trap, above-mentioned, it was abandoned. I shall presently advert to 

 other coal adventurers in this district, p. 328. 



Similar alternations of flagstone, containing the Asaphus Buchii, with layers of slaty felspar rock 

 inclosing much green earth, are found at Upper Gilwern on the elevated southern slopes of the 

 Gelli, where both these varieties have been long quarried as tile- stones, the coarser or refuse beds 

 serving as wall-stones. In the bold promontories which run out from these central masses to the 

 north-east towards Llandegley, particularly on their north-western slopes, are many alternations of 

 stratified trap and sandstone charged with casts of Caradoc shells. (See PI. 33. fig. 6.) A section 

 from the north-western foot of these ridges exhibits 



1st. Overlying dark shale, with slightly calcareous nodules dipping 20° N.N.W. (base of the 

 Upper Silurian Rocks.) 



1 This species of Graptolite differs from the G. Ludensis of the Lower Ludlow Rock. (See p. 206. and PI. 26.) 



