Physical Geology of the Dingle and Iveragh Promontories. 595 
newest of the enclosed Silurian fragments, because the fossils 
occurred in the pebbles and not in the matrix. 
The very existence of this conglomerate appears to prove 
incontestably the co-existence of denudation, which is the only 
absolute test of discordance. It shows that a varied series of beds, 
including metamorphic rocks, and others with Caradoc-Bala and 
Upper Silurian fossils, were undergoing destruction while it was 
being formed, and it points to the probability that some part of the 
Dingle beds is not so completely conformable to the Silurian below 
as has been supposed. That this older unconformity should have 
escaped detection cannot be considered strange, if it is contended 
that the discordance between the Carboniferous rocks of Sneem 
and the Glengariff beds has for years eluded observation, indeed, 
it would appear that the evidence in favour of discordance below 
the horizon of the Parkmore conglomerate, is stronger than that 
for the unconformity at the base of the Carboniferous beds of 
Kenmare river and estuary. 
The discordance connected with the Parkmore conglomerate 
does not invalidate the supposition that the bed itself may be- 
long to some part of the Upper Silurian series, if the institution 
of a newer group intermediate between Silurian and Lower 
Carboniferous should be undesirable. The unconformity might 
of course have been very local, and might occur anywhere between 
the highest intercalated bed with Silurian fossils and the con- 
glomerate itself. Regarding this break as possible in some part 
of the Dingle-Glengariff series, though unrecognizable among its 
parallel layers, it follows that some conglomerate bed in the 
upper part of the Dingle-Glengariff series of Iveragh, may also 
mark an unconformity equally obscure, or that this might occur 
even in the absence of such a bed in that region. Hence when 
ill-defined or invisible unconformities are possible in great series, 
marked by steady succession, amounting to a monotony of similar 
alternations, we must hold ourselves ready for surprise, and 
not count too confidently upon either general or detailed appear- 
ances, unless they are those of actual or gradual transition, 
which could not have occurred otherwise than tranquilly, or 
those of absolute unconformity, accompanied by discontinuous 
succession and palpable traces of co-existent denudation, which 
