458 PROFESSOR GEIKIE ON THE 
The size of necks varies from only a few yards up to more than a mile 
in diameter. In the east of Fife, so remarkable for the number and perfect 
preservation of these features of volcanic action, one of the smallest and most 
completely exposed necks occurs on the shore at Newark Castle, near St 
Monans. It measures only 60 yards in length by about 37 yards in breadth. 
A ground-plan of it is given in fig. 11, p. 468. Some remarkably small 
necks may also be seen on the Haddingtonshire coast, particularly in the 
neighbourhood of Dunbar. One of the largest in central Scotland is that 
already referred to as occurring among the Campsie Hills between Fintry 
and Lennoxtown. It is upwards of a mile broad, and is surrounded by other 
minor necks, several of which form prominent hills. 
Materials filling Necks.—These consist of (1) non-volcanic, and (2) volcanic 
rocks. 
1. In some minor necks the vent las been entirely or in great part filled 
with angular debris of the ordinary rocks of the neighbourhood. In the 
western neck on the Largo shore, for example, which rises through the red 
rocks of the upper Coal-measures, the material consists largely of fragments of red 
sandstone, clay, and shale. Some small necks, exposed in the ironstone workings 
near Carluke, were found to be filled with debris of black shale and ironstone. 
At Burntisland fragments of the well-marked cyprid limestone and _ shale 
abound. Between Elie and St Monans the tuffs are sometimes almost wholly 
composed of debris of black shale and encrinal limestone. At Niddry, in Lin- 
‘lithgowshire, large blocks, several yards in length, and consisting of different 
layers of shale and cement-stone, may be seen imbedded at all angles in the tuff. 
Where in these minor vents we encounter only the debris of non-volcanic 
rocks, we may infer that the volcanic action was limited to the explosion of 
steam whereby the rocks were dislocated, and an orifice communicating with 
the surface was drilled through them. No true volcanic rock in these cases 
appeared, but the pipes were filled up to perhaps not far from the surface by 
the falling back of the shattered debris. A little greater intensity or farther 
prolongation of the volcanic action would bring the column of lava up the 
funnel, and allow its upper part to be blown out as dust and lapilli ; while still 
more vigorous activity would be marked by the rise of the lava into rents of 
the cone or its actual outflow at the surface. Every gradation in this scale of 
progress may be detected among the Carboniferous volcanoes of this region. 
But though large cones might be built up by the long-continued emission 
of volcanic products, the first stage in these, as in the minor vents, must always 
have consisted in the perforation of the solid crust by explosion, and the 
consequent production of debris from the disrupted rocks. We may therefore 
expect that underneath the pile of thoroughly volcanic ejections traces of the 
first explosion must exist. I have been much struck with the fact that in the 
