Coal 

 Measures. 



Green — Carboniferous Rocks of N. Wales. 13 



notice. The upper beds of the former were in places full of small 

 pebbles of white quartz, and the bed (No. 4) seemed at times to pass 

 into a limestone. 



The sandstone (No. 4) forms a ridge to the east of the limestone 

 cliffs, and if we follow this northwards for a couple of miles or so we 

 come to a deep valley running down by Tyfynuchaf, along which the 

 rest of the sandstone group is laid open in the brook course, showing 

 us the following beds : — 



Section No. 2. (Beds in ascending order.) 



1. Sandstone (No. 4) of the former section. 



2. Gap, no section. 



3. Thinly bedded, shivery, cream-coloured rock, with a smooth marly 



fracture, (Productus, SpiriferJ. 



4. Gap, no section. 



5. Hard, finely-grained, light-coloured grit. 



6. Short gap, no section. 



7. Hard, grey, sandy shale. 



8. Hard finely-grained grit. 



9. Black shale, about fifteen feet thick, with a band of earthy limestone 



containing Productus, Spirifer, and Polypora. 



10. Closely-grained grit, some of it coarse. 



11. Very coarse, massive, rough grit, and conglomerate, containing 



much felspar, the decomposition of which makes the rock 

 crumbly. 



12. Dark shale. 



13. Coal, with Ganister floor. 



14. Hard closely-grained sandstone. 



The thickness of the beds, from No. 1 to 11 inclusive, is shown by 

 the sections of the Geological Survey to be between 800 and 1000 

 feet. 



About three miles east of Llangollen I got a good section of the 

 bed No. 11, and there a coal about 1ft. Gin. thick lay very close on 

 the top of the grit. 



These were all the observations I was able to make, and I grant 

 they are scanty enough, but the characters of some of the rocks are 

 so marked that I felt sure I recognised in them some well-known 

 acquaintances of Lancashu'e and North Staffordshire. 



And first, No. 11 has all the distinguishing marks of the Eough 

 Eock of those counties, and it has besides lying upon it a coal which 

 may correspond to the Peatheredge Coal of Lancashire. The highly 

 felspathic character of the bed is the guide I trust to most, but be- 

 sides that there was a likeness not easy to describe in words, but 

 perceptible to a practised eye. 



I failed, however, to find among the sandstones below this bed 

 anything that bore a resemblance to the lower gritstones of Lan- 

 cashire ; all the grits of the Welsh section, from No. 10 downwards, 

 had a common stamp, were very closely grained, highly quartzose, 

 rung under the hammer, and broke with a clean, bright fracture. 

 In this respect they agree very well with the shape which the Yore- 

 dale Sandstones wear in the neighbourhood of Leek and Congleton,i 



^ See "Geology of the countr / round Stockport, Macclesfield, Congleton, and 

 Leek." (Memoirs of the Geological Survey of Great I3ritain.) p. 17. 



