CHAP. XVI 
LITERATURE OF THE SUBJECT 
269 
structure of the country. Probably in 1820 he published in Prencb his 
now classic Essai} The value of this work as an original contribution 
to the geology of the British Isles lias probably never been adequately 
acknowledged. Por this want of due recognition the author himself was no 
doubt in some measure to blame. He refers distinctly enough to various 
previous writers, notably to Jameson and Macculloch, but lie mingles the 
results of his own personal examinations with theirs in such a way that 
it is hardly possible to ascertain what portions are the outcome of his own 
original observations. Less credit has accordingly been given to him than 
he 'could fairly have claimed for solid additions to the subjects of which 
he treated. In the later years of his life I had opportunities of learning 
personally from him how extensive had been his early peregrinations in 
Scotland, and how vivid were the recollections which, after the lapse of half 
a century, he still retained of them. Judged simply as a well-ordered 
summary of all the known facts regarding the geology of ScoBand, his 
Essai must be regarded as a work of very great value. Especially important 
is his arrangement of the volcanic phenomena of the country, which stands 
far in advance of anything of the kind previously attempted. Under the 
head of the “ Terrain Volcaiiique,” he treats of the basaltic formations, dis- 
tinguishing them as sheets (nappes, coulees) and dykes ; and of the felspathic 
or 'trachytic formations, which he subdivides into phonolites, trachytes, 
porphyries (forming mountains and also sheets) and felspathic or trachytic 
dykes. In the details supplied under each of these sections he gives facts 
and deductions which were obviously the result of his own independent 
examination of the ground, and he likewise marshals the data accumulated 
by Jameson, Macculloch and others, in such a way as to present a more 
comprehensive and definite picture of the volcanic phenomena of Scotland 
than any previous writer had ventured to give. 
The account which Bond wrote of the Old Bed Sandstone and its 
associated igneous rocks marked the first great forward step in the investiga- 
tion of this section of the geological record. He was the earliest observer to 
divide what he calls the “ roches feldspathiques et trappeennes ” into groups 
according to their geological position and mineralogical character, and to 
regard them as of igneous origin and of the age, or nearly of the age, of the 
red sandstone of Central Scotland. -m i t> i 
Of later writers who have treated of the volcanic rocks of the Old Bed 
Sandstone my old friend Charles Maclaren deserves special recognition. 
His survey and description of the Pentland Hills embodied the first detailed 
and accurate investigation of any portion of these rocks, and his Geology 
1 E,saigiolomucsaTlEcosse{V^vi^-, no date, Imt probably about 1820) He acknowledges 
his indebteduess to .lamesou, whoso denionstratiou.s of the geology ol the kduihurgh district he 
partly reproduced in liis book. .lamesoii’s early writings in the Wernerian Memoirs and in sepa- 
rate work.s were mere mineralogical or “gcognostical” descriptions. ni.s later lectures became 
more valuable hut were never published, save indirectly in .so far as they influenced the opinions 
of his impils who pnhii.shed writings on the same subjects. See, for instance. Hay Cunningham .s 
Geology of ike Lolhians, p. .09, footnote. Compare an article on Boue, Edinburgh Review for May 
1823 (vol. xxxviii. p. 413). 
