452 PROFESSOR GEIKIE ON THE 
In the attempt to ascertain the geological horizon of these volcanic rocks, 
as we are deprived of the assistance which interbedded sheets afford, we must be 
content to be able to fix certain limits of time within which the eruptions must 
have occurred. From St Andrews to Elie a chain of vents may be traced, 
having the same general characters, and piercing alike the Calciferous Sandstones 
and the older part of the Carboniferous Limestone series. That these vents must 
in many cases be long posterior to the rocks among which they rise, is indicated 
by some curious and interesting kinds of evidence. They are often replete 
with angular fragments of shale, sandstone, and limestone, of precisely the same 
mineral characters as the surrounding strata, and containing the same organic 
remains in an identical state of fossilization. It is clear that the rocks must have 
had very much their present lithological aspect before the vents were opened 
through them. Again, the vents may often be observed to rise among much 
contorted strata, as for example along the crest of a sharp anticlinal arch, or 
across a synclinal basin. The Carboniferous rocks must thus have been 
considerably plicated before the time of the volcanic eruptions. In the next 
place, the vents often occur on lines of dislocation without being affected 
thereby. They must be posterior, however, not only to these dislocations, but 
also to much subsequent denudation, inasmuch as they overspread the rocks on 
each side of a fault without displacement. Hence we conclude with confidence, - 
that the great period of volcanic activity in the East of Fife must have been 
posterior to most, if not all, of the Carboniferous period. 
In the neighbourhood of Largo, further important evidence is presented, 
confirming and extending this conclusion. The highest member of the upper 
Coal-measures, consisting of various red sandstones, with red and purple clays, 
shales, thin coals, and ironstones, is prolonged from the Fife coal-field ina 
tongue, which extends eastward beyond the village of Lower Largo. It is 
well displayed on the shore, where every bed may be followed in succession 
along the beach for a space of nearly two miles. Two volcanic necks, presenting | 
the same features as those which pierce the older portions of the Carboniferous 
system to the east, rise through these red rocks. We are thus carried not only 
beyond the time of the Carboniferous Limestone, but to the close of the very 
latest stage of the Carboniferous period in central Scotland. Connected with — 
these and other vents farther north, there isa large area of tuff which has been 
thrown out upon the faulted and greatly denuded Carboniferous rocks. It may 
be traced passing from the red upper Coal-measures across the large fa t 
which here separates that formation from the Carboniferous Limestone, and 
extending inland athwart different horizons of the latter series. Outlying 
fragmentary cakes of it may be seen resting on the upturned edges of the sand- 
stones, shales, and coal-seams, even at a distance of some miles towards the 
north-west, proving that the fragmentary materials discharged from 
‘ 
ee i i 
