CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 483 
which led to the spread of a marine and limestone-making fauna over much 
- of central Scotland affected also this volcanic district. The limestones extended 
over the submerged lavas and tuffs, which, however, in spite of the subsidence, 
continued for some time to be poured forth until the volcanic activity at last 
ceased, and the whole area went down beneath a deep mass of Carboniferous 
deposits. 
Numerous illustrations might be taken from Linlithgowshire showing a 
similar volcanic progress contemporary with ordinary quiet sedimentation. 
Two examples may suffice, one presenting intercalations of tuff, the other 
associated bands of lava. In fig. 22, we observe at the base a black shale (1) 
of the usual type. It is covered by a bed of nodular 
bluish grey tuff (2) containing black shale fragments. 
_ A second black shale (3) is succeeded by a second 
thin band of pale yellowish fine tuff (4). Black shale 
(5) again supervenes, containing rounded fragments of 
tuff, perhaps ejected lapilli, and passing up into a layer 
of tuff (6). Itis evident that we have here a continuous 
deposit of black shale which was three times inter- 
rupted by showers of volcanic dust and stones. At Fig. 22.—Section in old quarry, 
the close of the third interruption, the deposition of ee eee aio 
the shale was renewed and continued, with sufficient °° 
slowness to permit of the segregation of thin seams and nodules of clay iron- 
stone round the decomposing organic remains of the muddy bottom (7). A 
fourth volcanic interlude now took place, and the floor of the water was once 
more covered with tuff (8). But the old conditions of deposit were immediately 
afterwards resumed (9); the muddy bottom was abundantly peopled with ostra- 
cod crustaceans, while many fishes, whose coprolites have been left in the mud, 
haunted the locality. At last, however, a much more serious volcanic 
explosion took place. A coarse agglomeratic tuff (10), with blocks sometimes 
nearly a foot in diameter, was then thrown out, and overspread the lagoon.* 
A second example from Linlithgowshire (fig. 23) brings before us a 
volcanic episode of another form in the history of the Carboniferous Lime- 
stone. At the bottom of the section a pale amygdaloidal, somewhat altered 
basalt-rock (A) marks the upper surface of one of the submarine lavas 
of that period. Directly over it comes a bed of limestone (B) fifteen feet 
thick, the lower layers of which are made up of a dense growth of the 
thin-stemmed coral Lithostrotion irregulare. The next stratum is a band 
of dark shale (C) about two feet thick, followed by about the same thickness 
of an impure limestone with shale seams (D). The conditions for coral and 
crinoid growth were evidently not favourable, for this argillaceous limestone 
* See “Geological Survey Memoir of Edinburgh,” p. 45. 
