CHAP. XXVIII 
PUYS OF THE FIRTH OF FORTH 
463 
streaks of coal. Numerous epiphytic ferns grew on the subaerial stems and 
branches of the lycopodiaceous trees. Large coniferae clothed the higher 
grounds, from which the streams brought down copious supplies of sediment, 
and whence a flood now and then transported huge prostrate trunks of pine. 
In the lagoons animal life abounded. Cyprids swarmed to such a degree as 
to form by their accumulated remains bands of limestone, which in the well- 
known Burdiehouse seam sometimes attain a thickness of 70 feet. Fishes 
of many genera haunted the waters, for their scales, bones and coprolites are 
found in profusion among the shales and limestones. 
When the puys began their activity, this district was gradually d(;tted 
over with little volcanic cones. iVt the same time it was affected by the 
general movement of slow subsidence which embraced all Central Scotland. 
Cone after cone, more or less effaced by the waters which closed over it, was 
carried down and buried under the growing accumulation of sediment. New 
vents, however, continued to be opened elsewhere, throwing out for a time 
their showers of dust and stones, and then lapsing into cpiiescence as they 
sank into the lagoon. Two groups of volcanoes emitted streams of lava and 
built up two long volcanic ridges — those of Fife and West Lothian. 
The occasional presence of the sea over the area is well shown by the 
occurrence of thin bands of limestone or shale, containing such fossils as 
species of Ortlwccras, Bellerophon and Hiscina, which sullice to prove the 
strata to be stratigraphieal equivalents of the Lower Limestone shale, and 
part of the Carboniferous Limestone of England (Fig. 170). Yet the 
general estuarine or freshwater character of the accumulations seems satis- 
factorily established, not only by the absence of undoubtedly marine foians 
from most of the strata, but by the abundance of cyprids and small ganoids, 
the profusion of vegetable remains, and the occasional seams of coal. 
The portion of the Forth basin within which the puys are displayed 
extends from near Leven in Fife, on the north, to Crosswood Burn near the 
borders of Lanarkshire, on the south, a distance of about 3 G miles, and from 
near Culross in Fife and the line of the Almond Biver between Stirlingshire 
and Linlithgowshire, on the west, to the island of Inchkeith on the east, a 
distance of about 16 miles (Map IV.). But these limits do not precisely mark 
the original boundai'ies of the eruptions. To the north and south, indeed, 
we can trace the gradual dying out of the volcanic intercalations, rxntil we 
reach ground over which no trace of either lavas or tuffs can be detected. 
To the east, the waters of the Firth conceal the geology of a considerable 
area, the island of Inchkeith with its bedded lavas and tuffs showing that 
these rocks extend some way farther eastwards than the position of that 
island. But in Midlothian there is no evidence that any of the puy-eruptions 
took place to the east of the line of the Pentland Hills. On the west side, 
the volcanic rocks dip under the Millstone Grit and Coal-measures, so that 
we do not know how far they extend in that direction. But as the Carbon- 
iferous Limestone series, when it rises again to the surface on the west side 
of the Stirlingshire coal-field, is destitute of included lavas and tuffs, the 
westward limit of the eruptions cannot lie much beyond the line of the Eiver 
