458 
THE CARBONIFEROUS VOLCANOES 
BOOK Vi 
esen es remark their capricious distribution. Their occurrence seems to 
lave tittle or no relation to the measure of volcanic energy as manifested 
m superhcial eruptions. Thus in the north of Ayrshire, where a long 
band ot lavas and tulfs, pointing to vigorous activity, lies at the top of the 
karboniterous Limestone series, and where the strata underneath it are 
abundantly exposed at the surface, the sills occur as thin and inconstant 
bands in the central and eastern parts of the district only. The bedded 
avas and tuffs at the head of the Slitrig Water have no visible accompani- 
ment ol sills.^ On the other hand, in the Edinburgh and Burntisland 
f m ^ proportion to the amount of bedded lavas and 
u s, while in the Bathgate and Linlithgow district, where the superficial 
eruptions were especially vigorous and prolonged, the sills are of trifling- 
extent. ” 
It would seem from these facts tliat the extent to which the crust of 
the eartli round a volcanic orifice is injected with molten rock, in the form 
of intrusive sheets between the strata, does not depend upon the energy of 
tie volcano as gauged by its superficial outpourings, but on otlier considera- 
tions not quite apixarent. Possibly, the more effectively volcanic energy 
expelling materials from the vent, the less opportunity was 
attorded for subterranean injections. And if the protrusion of the sills took 
place after the vents were solidly sealed up with agglomerate or lava, it 
vvoii d doubtless often be easier for the impelled magma to open a way for 
Itself laterally between the bedding-planes of the strata than verticallv 
througli the thick solid crust. The size and extent of the siUs may thus 
be a record of the intensity of this latest pliase of the volcanic eruptions 
^ Losses. The rounded, oval or irregularly shaped masses of igneous rock 
included under this head are found in some cases to be only denuded domes 
ot sills, as, for example, in the apparently isolated patches in the oil-shale 
Fi(i. 167.— Boss of diabase cutting the Burdieliouse Limestone and sending sills and veins into the 
overlying shales. Railway cutting, West Quarr}-, East Calder, Midlothian. 
I . Burdiehonsc LiinestoiiB ; 2. Shales ; S. Diabase. 
district of Linlithgowshire, which have been found to unite under ground. 
(Compare lig.^ 157). In other instances, bosses possilily, or almost certainly, 
mark the position of volcanic funnels, as at the Castle Bock of Edinburgh, 
Duiiearn Hill, Burntisland, and Galabraes, near Bathgate. But many 
examples occur which can only be regarded as the exposed ends of irregular 
bodies of molten material which has been protruded upwards into the 
