68 
THE PERMIAN VOLCANOES 
BOOK VII 
detail for the Geological Survey, entirely confirming the observations of 
Maclaren. 1 In the end it seemed to me that the interval between the two 
epochs of volcanic activity might not be so great as Forbes had supposed ; 
and after tracing the Permian vents of Ayrshire, I came to the conclusion 
that the younger unconformable agglomerate of Arthur Seat was not im- 
probably Permian. 
The older volcanic series of this hill has been broken through by the 
agglomerate which occupies a true neck, and is abruptly marked off' from all 
the rocks older than itself. There is no trace of any of the older lavas or 
tuffs thickening towards this vent. On the contrary they are completely 
truncated by it, and their outcrops on the north side reappear from under 
the agglomerate on the south side. Their escarpments are wrapped round 
by the agglomerate which likewise fills the head of the hollow that had 
been previously worn by denudation out of the stratified deposits between 
the oldest lavas. There is thus a violent unconformability between the 
later and the older volcanic rocks of Arthur Seat. 
The length of time indicated by this stratigraphical break must be great. 
There is no known discordance in the Carboniferous system of the Lothians, 
yet the Coal-measures, Millstone Grit, Carboniferous Limestone series and 
much of the Calciferous Sandstones were stripped from this hill before the 
eruption of the agglomerate. It will be shown in the secpiel that a nearly 
similar amount of denudation preceded some of the probably Permian 
eruptions of Fife. 
The agglomerate contains abundant fragments of the older volcanic 
series. Its matrix is a dull red gravelly detritus, crowded with blocks 
of all sizes up to a yard or more in diameter. It is pierced by a 
column or plug of basalt, which sends veins into it, and rises to the apex ot 
the hill. A beautiful olivine -basalt forms the lateral mass of the Lion’s 
Haunch, which rests on the agglomerate. 
In general characters the agglomerate of Arthur Seat resembles that of 
some of the younger vents of Fife which pierce the Coal-measures and are 
Fig. 207. — Section showing the relations of the later rocks of Arthur Seat. 
1. Grey and reddish sandstones and shales (Calciferous Sandstones); 2. The lava of the Long Row: the oldest of 
the Carboniferous volcanic series; 3. Tuffs of the Dry Dam; 4. Columnar basalts overlying the tuffs; 5. 
Andesite lavas of the eastern half of Arthur Seat ; 0. SilL of Heriot Mount ; 7. Sill of Salisbury Crags ; 8. Sill 
of the Dasses. These complete the Lower Carboniferous volcanic series (compare Fig. 112). 1). White sand- 
stones and black shales, upper division of the Calciferous Sandstones; 10. Younger volcanic agglomerate 
resting on the denuded ends of the older volcanic series ; 11. Basalt of the summit sending veins into the 
agglomerate ; 12. Basalt of the Lion's Haunch. 
connected with tuffs that lie unconformably on the Carboniferous Limestone. 
On these various grounds I think that it may be reasonably assigned to the 
same geological period. 
1 Sheet 32, Geol. Survey of Scotland and descriptive Memoir. See also Rep. Brit. Assoc. 1867, 
address Geol. Sect., and Murchison’s Silm-ia, 4th edit, p. 331. 
