CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 441 
I, STRATIGRAPHY. 
A. THE CARBONIFEROUS STRATA OF THE BASIN OF THE FIRTH OF ForTH. 
The Carboniferous system of Central Scotland consists of the following 
subdivisions :— 
Upper red sandstones, nearly devoid of coal-seams. 
Coal-measures.. | PP é , y al-see 
Coal-bearing sandstones, shales, &c. (upper or Flat coals). 
Millstone Grit. Thick white and reddish sandstones and grits. 
Sandstones, shales, &c., with coal seams and three thin 
seams of encrinal limestone. 
Sandstones, shales, &c., with numerous seams of coal and 
ironstone (lower or Edge coals). 
(. Thick encrinal limestones, with some seams of coal. 
Carboniferous Limestone 
Series. 
White sandstones, oil-shales, some thin coals, and lime- 
stone (Burdie House). 
Red and grey sandstones and cornstones (Upper Old Red 
Sandstone) resting unconformably on Lower Old Red 
Sandstone. 
Calciferous Sandstone 
Series. 
At the outset it deserves to be kept in view that not only the basin of the 
Forth but the whole of central Scotland had already, long before the Carboni- 
ferous period, been the scene of some of the most stupendous volcanic eruptions 
which have been chronicled among the rocks of Great Britain. During the time 
of the Lower Old Red Sandstone the wide lake or inland sea which extended 
between the base of the Highland mountains and the Southern uplands was 
marked by two long lines of volcanic vents, from which prodigious volumes of 
lava and ashes were emitted. Even now, in spite of all denudation and dis- 
location, more than 5000 feet of volcanic material can be measured at the 
northern end of the Pentland Hills without reaching the top. In the Ochil 
Hills a depth of more than 6000 feet of similar rocks can be seen, and yet 
the bottom is not reached. Full details regarding these volcanic masses will 
be given in the second part of my Memoir on the Old Red Sandstone of 
Western Europe. In the meantime it is evident, that in tracing the history of 
the Carboniferous volcanoes, we must regard them as the diminished successors 
of an earlier series in the same region. That earlier series, however, seems to 
have been entirely closed long before the oldest of the Carboniferous eruptions. 
The two volcanic groups of rock are separated by a strong unconformability 
and extensive denudation, doubtless indicative of an interval of protracted 
duration. 
VOL. XXIX. PART I. 5X 
