WATSON — THE H.KM.VTITE DEPOSITS OF GLAMORGANSHIRE. 
253 
unproductive region relates only to the trouglis or positions near to 
the synclinal axes, and to whicli the exoteric agents, which aided 
mainly in the deposition of the ironstone, could never possibly have 
penetrated. 
On the statement of tliis fact, that these veins of hfEinatite may be 
considered superficial, the question of origin next arises. And hei"e is 
immediately opened to us the wide inquiry of the relationship of 
mineral veins to the rocks which inclose them. With veins filled 
with other ores than those of iron, the origin of the metallic accu- 
mulations may, in most cases, be referred to cavises acting from 
distant centres in the interior, assisted by tliose subterranean changes 
which are the universal result of the calorific and electrical agents 
that are always at work in the earth's crust. 
In a few words, the origin of these veins may be considered esoteric, 
or produced from within. With iron, however, in nearly all cases, 
an external derivation must be sought. The great solubility of its 
salts and chemical combinations, their affinity, and the proneuess of 
the metal itself to enter into union with substances with which it may 
have newly come in contact, gives to iron in its various forms a more 
world-wide distribution than is perhaps possessed by any other 
metallic mineral. Its local accumulation will therefore probably be 
the result of its chemical segregation and the nature of its combina- 
tions ; in other words, the particular class of oi-e will be governed 
by the mineral character of the transported matter, those portions 
which do not separate as ore solidifying into the vein-stones, or 
"gangue," which may either be amorphous or crystallized, according 
to circumstances. 
In the Llanharry district there is a bed of haematite five feet in 
thickness, of the same mineralogical character as the Llantrissant 
deposit, and occupying a similar geological position in the limestone. 
This bed has been anciently worked to some extent at Lleche, and, 
from the form of tlie chambers, or " stalls," and the narrow pit by 
which access was gained to the vein, probably by the Romans, 
who certainly were acquainted with the existence of the ore in the 
district. Some coarse red pottery, of undortbted Roman manufac- 
ture, was found a few years since buried in a small pit made in 
the bottom of an ancient stall-working at Ty-Ischaf. The pottery, 
VOL. II. 
