646 MR ARCHIBALD GEIKIE ON THE CHRONOLOGY 
intervals all over the Lothians, has long been known as the limestone of Burdie- 
house. 
Some time before, and also during the formation of this calcareous seam, the 
voleanic forces, which had been at rest for a considerable period, broke forth again 
with great energy. There were at least two areas of eruption perfectly distinct 
from each other, alike in the character and amount of the material ejected. 
By much the most vigorous action was that displayed throughout the region 
from North Berwick to Dunbar, the long line of cliffs between the two towns still 
bearing forcible evidence of the fact. Immense quantities of red felspathic dust, 
mingled with stones of all sizes, up to a yard or more in diameter, were thrown 
out over an area of at the least a hundred square miles. It was on a floor of this 
volcanic sediment that the Burdiehouse limestone in East Lothian was deposited. 
In many localities, as at Tantallon, the limestone is markedly ashy in composi- 
tion, and abounds with fine laminz of silica, disposed in crumpled layers, like the 
deposits of some thermal springs. Above it comes another series of ash-beds and 
conglomerates, succeeded by a still higher group of sheets of felstone, which, 
attaining a great thickness, form the chain of the Garlton Hills. With the ejec- 
tion of these lava-form traps, the igneous action in East Lothian appears to have 
ceased. A long bank of volcanic matter was left above the level of the surround- 
ing water, and not until the lower part of the Carboniferous limestone group 
began to be deposited was the inequality of surface removed, and the whole area 
reduced, by subsidence and deposition of fresh sediment, to one continuous level. 
Upon the submerged beds of felstone the limestones began to accumulate in undis- 
turbed succession; nor throughout the remainder of the Carboniferous rocks of 
East Lothian, is there any trace of further contemporaneous eruptions. 
I have said that the volcanic rocks of the Carboniferous system throughout 
the Lothians are of a markedly local character. This is nowhere more conspicu- 
ously displayed than on the horizon of the Burdiehouse limestone. In East 
Lothian, as we have seen, that bed accumulated amid the multiform ejections of 
an active volcano. In Mid-Lothian, however, the calcareous sediment gathered 
in undisturbed lagoons. Although the active volcanic focus of North Berwick 
was only twenty miles distant, yet, so far asthe evidence goes, no ash seems ever 
to have fallen among the cypris-shoals of Burdiehouse; but Stigmarie clustered 
thickly along the shallower swamps, and Lepidodendra shed their catkins among 
the matted ferns and rotting leaves that floated on the surface of the water, or 
sank among the limy mud at the bottom. 
On the west side of this undisturbed area, that is in Linlithgowshire, and the 
south-west of Mid-Lothian, there are traces of another centre of volcanic action 
on the same horizon with the ash-beds of North Berwick and Dunbar. A green, 
fine-grained felspathic ash is there found in several localities, below and above 
the Burdiehouse limestone; and at one locality (Corston Hill) a large sheet of 

