CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 481 
number of successive flows lie piled one above another without visible trace of 
intercalated fragmentary layers (fig. 21). This, so far as can be observed, is 
Fig. 21. —Section of four successive porphyrite lavas. 
East Linton, Haddingtonshire. 
the case in the Garlton Hills, though more numerous exposures might show 
thin interstratified tuff bands. In the Campsie Hills. also a considerable 
thickness of superposed lava-beds occurs without the intervention of any 
prominent tuff layer. These, however, are exceptional cases in this region, and 
they belong, as I have already pointed out, to a type of volcanic action which 
attained a great development during the time of the Calciferous Sandstones in 
the western and south-eastern parts of Scotland. 
Leaving out of account the Campsie and East Lothian districts, in the other 
large accumulations of volcanic material, lavas and tuffs are interstratified with 
each other as well as with the ordinary sedimentary strata of the Carboniferous 
system. Perhaps the most complete and interesting example of this association 
is to be found on the coast between Burntisland and Kirkcaldy. The total 
thickness of rock in that section may be computed to be about 2000 feet. Of 
this amount it will probably be a fair estimate to say that the igneous materials 
constitute four-fifths or 1600 feet. The lavas vary in character from a black 
compact columnar basalt to a dirty green cellular or slaggy anamesite. They 
may average about 15 or 20 feet in thickness. Columnar and amorphous beds 
often succeed each other without any tuff. But along the junctions of the 
separate flows, layers of red clay, like the bole between the basalts of the Giant’s 
Causeway, may frequently be noticed. The characteristic slaggy aspect of the 
upper parts of these ancient coulées is sometimes remarkably striking. It 
may be instructively contrasted with the close-grain of the upper and under 
margins of intrusive sheets. 
Throughout the Basin of the Firth of Forth the basaltic lavas forming 
interbedded sheets, present external distinctions which serve to mark 
them off from the intrusive sheets. They are never so largely crystalline, nor 
spread out as such thick sheets; are frequently slaggy, amygdaloidal, fine- 
grained, and porphyritic ; often decompose into a dull dirty-green fine-grained 
rock ; and where they form a thick mass, are composed of different beds, of 
varying texture. The microscope confirms and extends these distinctions. 
The number of intercalations of tuff in the admirable coast-section between 
Burntisland and Kinghorn is very great. Besides thicker well-marked bands, 
VOL. XXIX. PART I. 6 H 
