340 
VOLCANOES OF THE LOWER OLD RED SANDSTONE book v 
ant band of them is that which forms the highest member of the volcanic 
series. It consists of successive beds that vary from fine red mudstones up 
to volcanic breccias with blocks one foot or more in diameter. The 
materials have been derived from the explosion of andesitic lavas. Most of 
the lapilli are vesicular or amygdaloidal, and many of them have evidently 
come from vitreous scoriaceous lavas. Professor Geikie remarks that “ from 
their highly vesicirlar character, they might well have floated in water at 
the time of their ejection — they are in short mere cinders.” He could 
detect no trace of ordinary sediment in the matrix, the whole material 
being thoroughly volcanic in origin. 
The lavas, tuffs and agglomerates have been abundantly invaded by 
intrusive rocks, chiefly andesites.^ 
The agglomerates of this Berwickshire coast extend for a short way in- 
land from the Coldiugham and Eyemouth vents, but the fragmental material 
soon becomes finer and more water-rolled, and assumes a distinctly stratified 
structure, as it is gradually and increasingly interleaved with layers of 
ordinary sediment. Hence in passing towards the south-west, away from 
the coast-line, we are obviously receding from the vents of eruption and 
entering into the usual non-volcauic deposits of the time. That these 
deposits belong to the Lower Old Bed Sandstone was first ascertained 
during the progress of the Geological Survey in this district by the discovery 
of abundant plant-remains in the form of linear grass-like strips, and also, 
pieces of Pterygotus in some of the green shales interstratified among fine 
tuffs and ashy sandstones.'^ Before the volcanic detritus disappears from the 
strata as they are followed in a south-westerly direction, the whole series 
is unconformalily overlain by the Upper Old Bed Sandstone. The lower 
division of the formation is not again seen until it rises from under the 
soutliern margin of the plain of the Merse into the Cheviot Hills. 
About ten miles to the south-west of the large Coldingham neck the great 
boss of Cockburn Law and Stoneshiel Hill rises out of the Silurian rocks.^ 
Live miles still further in the same direction the group of the beautiful 
cones of Dirrington (Fig. 70) overlooks the wide Merse of Berwickshire,* 
and six miles to the north of these hills, in the very heart of Lammermuir,. 
lies the solitary boss of the Priestlaw granite.^ To these protrusions of 
igneous material reference has already been made as possible volcanic vents 
connected with the eruptions of the Lower Old Bed Sandstone. As regards 
their age they must certainly be younger than the Llandovery rocks which 
they disrupt, and older than the Upper Old Bed Sandstone, of which the- 
conglomerates, largely made from their debris, lie on them unconformably.. 
It seems therefore probable that these great bosses may form a part of the 
' See Prof. J. Geikie, op. oil. 
- “Geology of Eastern Bei'wickshire,” Mcvi. Geol. Sun Scotland (1864), pp. 26, 27, 57. 
^ See “The Geology of Eastern Berwickshire” (Sheet 34), Mem. Geol. Sun. Scotland (1864), 
p. 29. 
These hills are cliiety represented in Sheet 25. But see “The Geology of East Lothian, ^ 
Mem. Geol. Sun. Scotland (1866), p. 26. 
° “Geology of East Lothian,” Mem. Geol. Sun. Scotland, p. 15, and authorities there cited. 
