CHAP. XXIV 
373 
THE MIDLOTHIAN PLA TEA U 
peculiar lavas of the Garleton Hills form irregularly-uneven ground, rising 
to not more than 600 feet above the sea. They slope gradually down to 
the coast, where a succession of fine sections of the volcanic series has been 
laid bare for a distance of altogether about ten miles. Nowhere, indeed, 
can the phenomena of the plateau-tuffs and their association with the 
Carboniferous strata be so well studied as along the coast-lme from ISor i 
Berwick to Dunbar. Among the necks of this plateau distinguished for 
their size, coii.spicuous prominence and component materials, tlie mos im- 
portant are those that form the conical eminences of North Beiwick Law 
(Fig. 109), Traprain Law (Fig. 133), and the Bass Eock (big. 110). 
3. The Midlothian Plateau. — On the same general stratigraphical 
horizon as the other volcanic plateaux, a narrow band of lavas and tuffs can 
be followed from the eastern outskirts of the city of Edinburgh into Lanark- 
shire, a distance of about 23 miles. It is not continuously visible, often 
disappearing altogether, and varying much in thickness and composition. 
This volcanic tract, which may be conveniently termed the Midlothian 
Plateau, is the smallest and most fragmentary of all the series. Its most 
easterly outliers form Arthur Seat and Calton Hill at Edinburgh. Three 
miles to the south-west a third detached portion is known as Craiglockhart 
Hill. After another interval of ten miles, the largest remaining fragment 
forms the prominent ridge of Corstou Hill (Fig. Ill), whence a discon- 
tinuous narrow strip may be traced nearly as far as the Paver Clyde. 
The well-known Arthur Seat and Calton Hill have been fully described 
by Maclaren, and have been the subject of numerous observations by other 
geologists.® They have been likewise mapped in detail on a large scale by 
1 I formerly claBsed these emineiicea with the Pays, hut I am now of opinion that they ought 
rather to be regarded as fragments of a long and somewhat narrow plateau. Their ba^ic lavas 
and overlying sheets of porphyrite repeat the ii.sual sequence of the plateaux, which is not met 
with among the Puys. Hut, as will be pointed out in the sequel, Arthur Seat m long subsequent 
time became again the site of a volcanic vent. 
2 MaclareiTs aeology of Fife and the Lothinm, 1839, pp. 1-67 ; and Hay Cunningham, Mcm. 
Wer. Soc. vii. pp. 51-62. 'tIio plateau is represented in Sheets 24 and 32 of the Geological Survey, 
and Arthur Seat and Calton Hill will be found on Sheet 2 of the Geological Survey map ot 
Edinburghshire on tlie scale of 6 inches to a mile. 
