CHAP. XXVII 
VENTS OF THE SCOTTISH PUYS 
425 
that they must be later than the particular formations wliich they pierce. 
Some of them, as 1 shall endeavour to show, are in all probability of Permian 
age. But many, from their position with reference to the nearest inter- 
calated lavas and tuffs, are to be regarded as almost certainly belonging 
to the Carboniferous period. Tliose which are immediately surrounded by 
sheets of lava and tuff, similar in character to the mateidals in the vents 
themselves, may without hesitation be connected witb these sheets as 
marking the orifices of discharge. 
The vents of the pays are in general much less than those of the 
plateaux. Their smallest examples measure only a few yards in diameter, 
their largest seldom much exceed half a mile.’^ 
The dislocations of the Carboniferous system are probably on the whole 
later tlian its volcanic phenomena. It is at least certain that the lavas and 
tuffs of the puys have been extensively faulted, like the surrounding sedi- 
mentary strata, and the vents seldom show any apparent relation to faults. 
It may sometimes he observed, however, that the vents are arranged in lines 
suggestive of fissures underneath. A remarkable instance of the linear dis- 
tribution is furnished by the chain of necks which extends Irom the Cale of 
the Tweed at Melrose south-westwards across the watershed and down 
Liddesdale. The most notable part of this line lies among the uplands to 
the east of the Old Mosspaul Inn at the head of the Ewes Water. A string 
of masses of agglomerate has there solidified in a fissure among the Silurian 
greyw'ackes and shales, running in a north-easterly direction for several 
miles. The largest connected mass of agglomerate is 4700 feet long, and 
from ;350 to 600 feet broad (see No. 1 in Fig. 22). That this curious vent, 
or connected line of vents along a great fissure, belongs to the puy-eruptions 
of Liddesdale is shown hy the abundant fragments of yellow sandstone and 
cement-stone which occur in the agglomerate.^ 
Most frequently the vents are distributed irregularly in groups. As 
examples of this arrangement I may cite those of the west of life, of LVest 
Lothian and of the north of Ayrshire. 
A convenient classification of the vents may be made by dividing them 
into four grouj)S according to the nature of the material that now fills them : 
1st, Necks of non-volcanic debris ; 2nd, Necks of ttiff and agglomerate ; 3rd, 
Necks of similar materials, but with a central plug of basalt ; 4th, Bosses of 
hasalt or other lava, without agglomerate or tuff. 
^ The following measurements of necks belonging to the puy -eruptions in dilFereiit parts of 
Scotland are taken from the 6-inch Iiekl-nnip.s of the (leological Survey Saline Hill, Fife, 6000 x 
4000 feet ; Binn of Burntisland, 3.500 x 1500 ; Hill of Be.ath, Fife, 2900 x 1550 ; Binns Hill, Lin- 
lithgowshire, 4800x2200 ; Tor Hill, Eeele.smachan, Linlithgowshire, 1900 x 1000 (Fig. 155) ; Great 
Moo”, near Jlaiden Pap, Koxburgh.shire, 2600 x 2400 ; Tinnis Hill, Lidde.sdale, 1500 x 1000 ; Koaii 
Fell, Liddesdale, 300x200; Iladsgarth Burn, I.iddesdale, 250x200; Ilalbate Burn, 250x120. 
In some cases, especially in those of the larger uock.s, it is probable that the tuli belongs to more 
than one funnel. Thus the Biun of Burntisland almost certainly includes two necks, a smaller 
one to the west and a mncb larger one to the east. Saline Hill may also conceal more than one 
vent. But in the continuous mass of tulf at the surface it is at present impossible to determine 
precisely the number and boundaries ol the several orilices. 
- These facts were ascertained by Mr. Peach in m, upping the ground for the Geological Survey. 
See Sheet 17, Scotland. 
