Chap. IV.] 
THE BREIDDEN HILLS. 
81 
which cuts, as a dyke, through the Lower Silurian strata and has much 
altered them. At a little distance, however, from the trap-rock, those beds 
contain organic remains, some of them having particularly the Trinucleus 
concentricus or T. Caractaci (see PI. IV. f. 2-5). 
This prismatic igneous rock is largely quarried as a building-stone, like 
that of the Whittery Quarries. It is remarkable in having its light-green 
felspathic matrix abundantly speckled with minute kernels of calcareous 
spar, which being mixed with the finely aggregated felspar renders the 
rock a sectile and valuable freestone. 
Eruptive greenstones, as well as hypersthene rock, are seen to cut through 
Silurian strata near Old Radnor (Sil. Syst. p. 318) ; but as they are asso- 
ciated with strata of younger date than those we are now considering, they 
will be more appropriately mentioned in another chapter. 
On the flanks of the Carneddau Hills, between Llandrindod and Builth, 
there are irregular masses of igneous rock which have broken through 
and highly altered the Llandeilo Mags. Beautiful examples of this are 
seen on the banks and in the bed of the Wye, west of Builth. (See Sil. 
Syst. p. 332 et seq.) 
On this occasion one diagram only is selected from the plates of my large 
work, to show, first, how the strata of the Llandeilo formation alternate 
with bedded igneous rocks, b*, and, next, how they have been altered in 
contact with eruptive masses, *. It is in these black and hardened schists, 
along the lines of contact, that films of anthracite were found, which led 
credulous farmers to search for coal f. 
Section across the G-elli Hills. 
N,W. (From Sil. Syst. pi. 33. f. 5.) S.E. 
Llandrindod 
* * # # I 
b. Llandeilo Flags, b*. Llandeilo Flags with interpolated cotemporaneous felspathic 
ashes, &c. * Eruptive rocks. 
Another frequent result, in this district, of the intrusion of the igneous 
rock into the schists is the production of much sulphuret of iron, the 
decomposition of which mineralizes the various waters at Llandegley, 
t A full exposure of this folly was given in the ' Silurian System,' p. 328, with this diagram, repre- 
senting an actual search after coal (!) at a spot called Tin- y- Coed, thus: — 
