WATSON — THK niEMATITE DEPOSITS OP GLAMORGANSHIRE. 251 
masses, rendering them at the same time exceedingly hard to blast ; 
the " getting of the ore " being almost exclusively performed with gun- 
powder. In the small cavities or angles, where we might expect to 
find the botryoidal forms or "kidney-ore," none such occurs, but 
instead, as mentioned above, we have often magnificent specimens of 
rock-crystal, inclosing minute but very perfectly formed crystals of 
specular ore. The " raddle " or fine powdeiy micaceous ore, which 
soils the fingers on the most delicate touch, and which is always dis- 
tinctive of the Ulverstone hsematite, and some of the ores raised in 
North Wales, is uniformly absent, and in lieu of it the less coherent 
parts of the vein-stuff are represented by an ochraceous earth (argil- 
laceous hydrous sesqui-oxide of iron), which in wet weather works up 
to a stifi" red mud, but is far inferior in per-centage of iron to 
the Ulverstone " raddle," (anhydrous sesqui-oxide of iron), which, like 
the " smith-ore " of the Forest of Dean, is always of equal value with 
the more solid products of the veins. 
One of the most interesting lithological featui-es connected with 
these Llantrissant mines is the " yellow clay " (ochre). This mineral 
occurs in great abundance, " riding " the vein near the crop above the 
deposit, and is several yards in thickness : it is of a pale lemon-chrome 
colour, and I have little doubt might find use as a coarse pigment. 
It is probably a hydrate of alumina and silica, with hydrate of the 
sesqui-oxide of iron, and, mineralogically, the equivalent of " Limonite." 
In my paper upon the Ironstone Formation of the Forest of Dean* 
I have mentioned the circumstance that the upper portion of the 
"joints" which cut across the underlying limestone of the "mine- 
measures" is filled with a highly ferruginous marl, described as " clod- 
ore and I may here observe, that ochraceous earths are superficially 
common to most of the deposits of ironstone in the carboniferous 
limestone. The origin of these feiTuginous clays or marls must doubt- 
less be assigned to the introduction of the wasted alluvial matters 
derived from the weathering of the contiguous rocks, and their sub- 
sequent amalgamation with the ferriferous matters of the vein, but it 
is at least curious, that each dissimilar deposit of haematite has its 
own peculiar character of " clod " in the same way that the veins of 
' • Geologist, vol. i. p. 270. 1858. 
