WATSON — THE HiEMATITE DEPOSITS OF GLAMORGANSHIRE. 251 



masses, rendering them at the same time exceedingly hard to blast j 

 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 powdery micaceous ore, which 

 soils the fingers on the most delicate touch, and which is always dis- 

 tinctive of the Ulverstone haematite, and some of the ores raised in 

 North Wales, is uniformly absent, and in lieu of it the less coherent 

 parts of the vein-stufi" 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 features connected with 

 j these Llantrissant mines is the " yellow clay " (ochre). This mineral 

 I occurs in great abundance, " riding " the vein near the crop above the 

 I 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. 

 I It is probably a hydrate of alumina and silica, with hydrate of the 

 i 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 fermginous 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- 

 1 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. 



