12 D, C. DAVIES ON THE UPPER CARBONIFEROUS 



a quarter of an inch thick, with an underclay. This ring of coaly 

 matter thickens northward, so that at Hafod-y-bwch, it forms an 

 impure coal five inches thick. 



Above this group we reach a thin deposit of blue shale. This is 

 succeeded by a fire-clay four feet thick ; and this, in its turn, is sur- 

 mounted by a coal-scam sixteen inches thick, of fair quality. This 

 coal has a hard grey shale roof, which is a perfect storehouse of plant- 

 remains : a brief attempt was recently made to work the coal ; and 

 in doing so a fine calamite stem, twenty feet long and from twelve to 

 eighteen inches in diameter, was exposed in the roof shale. Pecopteris 

 {Bucklandi ?) abounds ; so also do Stigmarice and Lepidodendra of 

 various species. There are also Asterophyllites, Ncuropteris (cordata), 

 Araucaria, Stembergia and other plant-remains. In driving a road 

 through this shale some distance above the coal, there was found an 

 erect trunk of Catamites or Calamodendron gigas, which measures 

 eighteen inches across the base, and about six feet in length of which 

 was excavated and is preserved. This specimen retains portions of 

 the outer bark in a carbonized state. These fossiliferous shales are 

 covered by a hard grey rock locallj^ known as the " half-yard rock," 

 above which we reach about five yards of fire-clay, of which I wish 

 especially to remark that it contains numerous rounded balls of 

 limestone, which are imbedded throughout it. 



This thick clay is surmounted by a group of coals, of which the 

 following is a section. 



ft. in. 



Top.— Coal 2 6 



Dirt 7 



Coal 6 



Fireclay 10 



Coal 1 3 



Fireclay .„ 6 



Coal 6 



6 8 or Coal 4 ft. 9 in. 



A noticeable feature in this coal, which is worked and is now known 

 as the "Morlas Main," is the occurrence (rather too often) of 

 " brasses" which are exclusively the pyritized stems of Calamoden- 

 dron commune : many of these are very instructive specimens, which 

 show the original structure of the wood as well as of the inner and 

 outer bark. 



For a reason which will be obvious presently, I wish to call especial 

 attention to the almost unique mineral composition of these pyritized 

 stems. Mr. D. Hesketh Richards, of Oswestry, gives the following- 

 analysis of them : — 



Iron 30506 



Sulphur 34-864 



Carbonate of lime 25*500 



Other constituents not determined, but consisting 



for the most part of coal and insoluble matter. .. 9130 



100-000 



