268 
VOLCANOES OF THE LOWER OLD RED SANDSTONE 
BOOK V 
amount to many thousand feet in thickness ; yet from bottom to top they 
abound in evidence of shallow-water conditions of deposit. The terrestrial 
disturbances above referred to continued for a vast interval, and while, as 
already suggested, the doors of the basins sank, and the intervening tracts 
were ridged up, as the results of one great movement of the earth’s crust, 
the denudation of the surface of the land contributed to the basins such a 
constant influx of sediment as, on the whole, compensated for the gradual 
depression of their bottoms. 
We need not suppose that these movements of subsidence and upheaval 
were uninterrupted and uniform. Indeed, the abundant coarse conglomerates, 
which play so prominent a part in the materials thrown into the basins, 
suggest tliat at various intervals during the prolonged sedimentation 
subterranean disturbances were specially vigorous. But the occurrence of 
strong unconformabilities among the deposits of the basins sets this question 
at rest, by jn-oving that the terrestrial movements were so great as some- 
times to break up the door of a lake, and to place its older sediments on 
end, in which position they were covered up and deeply buried by the 
succeeding deposits.’ 
It is not suiqrrising to discover, among these evidences of great terrestrial 
disturbance, that eventually groups of volcanoes rose in long lines from the 
waters of most of the lakes, and threw out enormous quantities of lava and 
ashes over tracts hundreds of square miles in extent. So vast, indeed, were 
these discharges, across what is now the Midland Valley of Scotland, that the 
portions oi sheets ol lava and tuff visible at the surface form some of the 
most conspicuous ranges of hills in that district, stretching continuously for 
40 or 50 miles and reaching heights of more than 2000 feet above the 
sea. Exposed in hundreds of ravines and escarpments, and dissected by the 
waves along both the eastern and western coasts of the country, these 
volcanic recoi’ds may be studied with a fulness of detail which cannot be 
found among earlier Palreozoic formations. 
It might have been supposed that a series of rocks so well displayed 
and so full of interest, would long ei’e this have been fuUy examined and 
described. But they can hardly be said to have yet received, as a whole, 
the attention they deseiwe. Without enumerating all the writers who, each 
in his own measure, have added to the sum of our knowledge of the subject, 
I may refer to the labours of Jameson,^ Macknight® and Fleming,^ among 
the observers who began the investigation. But of the early pioneers, by far 
the most important in regard to the igneous rocks of the Old Bed Sand- 
stone was Ami Bond. While attending the University of Edinburgh, where 
he took the degree of AI.II. in the year 1816, he imbibed from Jameson a 
love of mineralogy and geognosy, and for several years spent his leisure time 
in personally visiting many parts of Scotland, in order to study the geological 
^ An nnconformability of this kind occurs between tlie south end of the Pentland Hills and 
Tinto in Lanarkshire, and another in Ayrshire. 
= Memoirs of the. Wernerian. Society, vol. ii. (1811), pii. 178, 217, 618 ; vol. iii. (1820), p. 220, 
3 Op. cit. vol. ii. pp. 123, 461. 
Op. cit. vol. i. (1808), p. 162 ; vol. ii. (1811), pp. 138, 339. 
