392 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
growth. A remarkable instance of this nature occurs in some bands of tuff 
in the volcanic group of the east coast of the Isle of Arran, first brought to 
notice by Mr. E. Wunsch,’^ and of which the plants have been so fully 
investigated by Professor Williamson.^ 
Plant-remains also occasionally occur in the stratified layers intercalated 
among the lavas and tuffs of tlie plateairx. Some of the best examples of 
tlieir occm’rence are to be found in the shales and tuffs interstratified among 
the enormous pile of volcanic material near Bowling. Not only does 
abundant vegetable debi'is occur distributed through the detrital strata in the 
volcanic series at that locality, but it is even aggregated into thin seams of 
coal which liave been examined and described by various observers.® It may 
£ w. 
Fio. 1*20. — Section across part of tlie Clyde Plateau to the west of Bowling (reduced from Sheet 6 
of the Florizontal Sections of the Geological Survey of Scotland). 
1. “ Ballagaii Beds” ; 2. White sandstone 5 8. Tuffs, tiOO feet thick, with a thin sheet of andesite ; 4. Andesite 
sheets, 500 feet ; 5. Stratified tuffs with thin coals, shales, fireclays and plant-reiuains, 500 or 000 feet ; 6 6. 
A series of andesite-lavas, about 1500 feet thick, enclosing a thin coal-seam at * ; 7. Stratified tuffs, 200 feet ; 
8. Shales with jdants and coaly seaius, 150 feet ; 9. Base of another andesite series, which must be some 
hundreds of feet thick. 10 and 11. Necks of agglomerate. 
be remarked tliat the pliiut remain.^ thus found intercalated iu the volcanic 
series, especially wlien they have been entombed in tuff, have often had 
their internal structure admirably preserved, the organic tissues having 
been delicately replaced by calcite or other petrifying medium. The 
remarkably perfect structure of some of these plants has been demonstrated 
by Professor Williamson, especially iu the case of the Arran deposit just 
referred to. Mr. John Young has also found the structure well preserved 
among the Sigillarim and Stigmarice that occur in the stratified intercalations 
between the lavas near Bowling. 
Upper Limits and Original Areas and Slopes of the Flatemix. — "Where 
tlie liigliest members of the volcanic series can be seen passing conform- 
ably under the overlying Carboniferous strata they are frequently found to 
be mainly composed of fine tuff’s, the last feeble efforts of the plateau- 
volcanoes having consisted in the discharge of showers of ashes. These 
materials were mingled with a gradually increasing proportion of ordinary 
mechanical sediment, wliich finally overspread and buried the volcanic tracts 
of ground, as these slowly sank in the general subsidence of the region. 
The characteristic corals, crinoids and shells of the Carboniferous Limestone 
begin to appear in these ashy sediments. There is thus an insensible 
passage from volcanic detritus into fossiliferous shales and limestones. 
' Trans, deal. Soc. (llasgnw, vol. ii. (1867) p. 97. Phil. Trans. 1871-1883. 
See in particular J. Young, Trans. Geol. Soc. Glasgow, vol. iv. (1874) p. 123. 
