CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 447 
in the Edinburgh district. These rocks, though they did not reach the surface, 
must be regarded as subterranean portions of the volcanic series. Besides the 
sheets and veins at Arthur Seat, numerous smaller portions occur near Loch- 
end, and underlying the city of Edinburgh. To the west an irregular belt of 
large sheets runs from the Water of Leith northwards into Fife. 
2. East Lothian District—This forms a very distinctly defined area of 
about 65 square miles. It includes the Garlton Hills, with a few outstanding 
eminences to the south of these heights, and most of the coast from near Dirleton 
to Dunbar. As shown in the fifth column (Plate X.), the volcanic masses, 
filling up most of the interval between the red sandstones and the base of the 
Carboniferous Limestone, must attain a thickness of possibly 1500 feet, though, 
owing to the paucity of sections, only an approximate estimate can be made. 
At the base of this thick pile of material lies a deep series of red and green 
tuff, resting upon red and white sandstones and red marls. These frag- 
mental accumulations are admirably shown along the coast to the west of 
Dunbar, and on both sides of North Berwick. Abundantly interstratified in 
some parts of the tuff are seams of sandstone, blue and green shale, cement- 
stone and limestone. One thick band of limestone may be traced from near 
Tynningham House to Whittingham—a distance of about four miles; another 
patch appears near Rockville House; and a third at Rhodes, near North 
Berwick. 
No fossils have been noticed in these limestones. The calcareous matter, 
together sometimes with silica, appears to have been supplied, at least in part, 
by springs, which may be looked upon as having formed part of the volcanic 
phenomena of the district. Parts of the limestone are vesicular, and contain a 
decayed zeolite, scattered crystals of pyrite, and cavities lined with dog-tooth 
Spar. Some portions give out a strongly foetid odour when freshly broken. 
After the cessation of the showers of ash and bombs, lava began to flow, 
and continued to do so with apparently little intermission until the mass 
of the Garlton Hills had accumulated. No thick zones of tuff, nor inter- 
stratified layers of sedimentary rock, can anywhere be seen, separating the 
successive lava-beds, though it must be owned that the sections of the rocks 
are few and unsatisfactory. The earliest lavas were dark red, strongly augitic 
porphyrites. But the remaining, and much the larger portion, were dull-red, 
purple, pink, grey, brown, yellow, and even white fine-grained porphyrites, and 
“claystones.” 
One of the most interesting features in this district is the occurrence of 
numerous old volcanic orifices round the margin of the area. On the coast, 
both to the west and east of North Berwick, they may be seen in the form of 
necks of agglomerate, basalt, or porphyrite. North Berwick Law is a conspicu- 
ous example, and the Bass Rock is probably another. A beautiful instance 
