364 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
meats ot different phases of volcanic action previous to tiie formation of 
the Coal-measures. His detailed descriptions of Arthur Seat and the rocks 
inmiediately around Edinburgh, which alone the work was originally in- 
tended to embrace, may be cited as models of exact and luminous research. 
Tlie portions referring to the rest of the basin of the Forth did not profess 
to be more than a mere sketch of the subject. 
A arious papers of more local interest, to some of whicli allusion will be 
made in the sequel, appeared during the next quarter of a century. But 
no systematic study of the volcanic phenomena of any part of Scotland 
was resumed until the extension in 1854 of the Geological Survey to the 
north of the Tweed Ijy A. C. llamsay. The volcanic rocks of the Lothians 
and Fife were mapped by Mr. H. H. Howell and myself. The maps of that 
district began to be published in the year 185 9, and the Jlemoirs two years 
later. In 1 8 6 1 , in a chronological grouping of the whole of the volcanic phe- 
nomena of Scotland, I gave an outline of the Carboniferous eruptions.^ By 
degrees the detailed mapping of the Geological Survey was pushed across the 
whole of the rest of the south of Scotland, and the Carboniferous volcanic 
rocks of each area were then for the first time carefully traced and assigned 
to their various stratigraphical horizons. In the following pages reference 
will be given to the more important features of the Survey maps and 
Memoirs. In the year 1879, availing myself of the large amount of 
information which niy own traverses and the work of the Survey had 
enabled me to acquire, I published a Memoir on the geology and petro- 
graphy of the volcanic rocks of the basin of tire Firth of Forth ; ^ and lastly, 
in my Bresidential Address to the Geological Society in 1892, I gave a 
surnrrrary of all that had therr beerr ascertained orr the srrbject of the volcanic 
rocks of Carboniferous time in the British Isles.® 
Two well-rrrarked types of volcarric accumrrlations are recognizable in 
the British Isles, which may be eoirveniently termed Plateaux and Prrys. 
1. Plateaux. — Iir this type, tire volcanic materials were discharged 
over wide tracts of country, so that they now form broad tablelands" or 
ranges of hills, reaching sometimes an extent of marry hundreds of square 
ririles and a tlrickrress of more than 1000 feet. Plateaux of this character 
ocerrr withirr the British area only irr Scotland, wdrere they are the pre- 
dominarrt phase of volcarric intercalations in the Carbemiferous system. 
It is noteworthy that the Carboiriferous plateaux appeared during a 
well-nrarked irrterval of geological time. The earliest exairrples of therrr date 
from the close of the Upper Old Bed Sarrdstone. They were all irr vigorous 
errrptiou during the tirrre of the Calciferous Sarrdstorres, but in no case did 
they survive irrto that of the Hrrrlet and later lirnestorres. They arc thus 
enrinerrtly eharircteristic of the earliest portiorr of the Carborriferous period. 
2. Pdys. — Irr this type, the ejections wore ofteir corrfirred to the dis- 
charge of a small arnourrt of fragnrentary materials front a single solitary 
1 Trans. Roy. Soc. Edin. vol. xxii. 2 2hid. toI. xxix. (1879), ]). 437. 
» Quart. Journ. Ckol. Soc. xlviii. (1892), p. 104. Tliis summary, with additional details and 
illustrations, i.s embodied in the text. 
