CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 473 
fig. 15. Immediately tu the east of the Saline Hill lies another eminence, known 
as the Knock Hill, which marks the site of another eruptive vent. A coal- 
Fig. 15.—Section across the Saline Hills, Fife. 
The thick parallel black lines mark the position of seams of coal and ironstone, some of which are worked under Saline 
Hill. TT, Tuff of the necks ; ¢, Tuff at a little distance from the cone, interstratified with the ordinary sedimentary 
beds ; B, Basalt. The larger eminence is Saline Hill, the lower is Knock Hill. 
seam (the Little Parrot or Gas Coal) is worked along its southern base, and is 
found to plunge down steeply towards the volcanic rocks. This seam, however, 
is not the same as that worked under the Saline Hill, but lies some 600 feet 
below it. Probably the whole of the Knock Hill occupies the place of a 
former vent. 
Many additional examples might be cited of partially uncovered volcanic 
cones still surrounded by their ejectamenta. Probably in most cases the upper 
loose portion of a cone would be washed down as the general subsidence of the 
region brought it within reach of the water. Hence the crater would disappear, 
and only such rounded cones would remain as those which have been exposed 
once more to view by the removal of the overlying Carboniferous formations. 
The subjoined diagram (fig. 16) may serve to show the stages in the gradual 
re-emergence of these buried cones. 
Fig. 16.—Diagram to illustrate how volcanic necks may be concealed and exposed. 
1, Tuff and basalt neck, still buried under the succeeding sedimentary accumulations; 
2, Tuff and basalt eone partially uncovered and denuded. 
Final Stages of Volcanic Activity in the Tuff-necks.—After the explosions 
‘ceased by which the vents were opened and the cones of debris were heaped 
up, heated vapours would in many cases, as in modern volcanoes, continue for 
a long while to ascend in the vents. The experiments of DAUBREE on the 
effects of water and vapour upon silicates under great pressure and at a low 
red heat, have shown how great may be the litholugical changes thereby 
superinduced. It is inconceivable, therefore, that the mass of tuff and lava 
VOL. XXIX. PART 1. 6F 
