64 
THE PERMIAN VOLCANOES 
KOOK VII 
In almost all cases, the necks of the Ayrshire region consist of a gravelly 
tuff or agglomerate, reddish or greenish in colour, made up of blocks of such 
lavas as form the bedded sheets, together with fragments of the stratified 
rocks through which the chimneys have been blown out. Thus, in some 
of the necks, pieces of black shale are abundant, as at Patna. In other cases, 
there are proofs of the derivation of the stones from much greater depths, 
as in the Green Hill of Waterside, where fragments of fine greywacke are 
not infreqent, probably derived from the Silurian formations which lie deep 
beneath the Carboniferous and Old Red Sandstone series. 
The fragmentary material of the necks is generally unstratified, but a 
rude stratification may sometimes be noticed, the dip being irregularly 
inward at high angles towards the middle of the vent. Tins structure, best 
Fig. 205. — Ground plans of Permian volcanic vents from the Ayrshire Coal-field. On the scale of 
six inches to a mile. 
]. Neele half a mile north-west from Dalmellington ; 2. Neck at Auchengee, four miles north-east from Patna; 3. 
Neck at head of Drumbowie Burn, five and a half miles due north from Dalmellington ; 4. Patna Hill, 853 feet 
above sea-level (for outline of this hill see the preceding Fig.); 5. Neck on Kiers Hill (1005 feet above tin- 
sea), two miles south from Patna, with lava adhering to part of the wall. 
seen in the vents of the Fife coast, as will be shown in the sequel, may be 
detected in some of the necks of the Dalmellington district. 
Occasionally some form of molten rock has risen in the funnel, and has 
partially or wholly removed or concealed the agglomerate. This feature is 
especially noticeable among the necks that pierce the Dalmellington coal- 
field. Portions of basic lavas traverse the agglomerate or intervene between 
it and the surrounding strata. These have probably in most cases been 
forced up the wall of the funnel, while here and there sills rim outward 
from the necks into the surrounding Coal-measures. Sometimes a thin sheet 
of lava, adhering to the wall of a funnel, may he the remnant of a mass of 
rock that once filled up the orifice. In one of the necks of the Muirkirk 
Coal-field, which v T as pierced by a mine driven through it from side to side, 
