CHAPTER XXIX 
THE CARBONIFEROUS VOLCANOES OF ENGLAND 
The North of England : Dykes, The Great Whin Sill— The Derbyshire Toadstones— 
T-lie Isle ol Mail — East Somerset — Devonshire 
1. THE NORTH OF ENGLAND 
The volcanic intercalations which diversify the Lower Carboniferous forma- 
tions of Southern Scotland extend hut a short way across the English 
Border, and although, over the moors and hills of the north of Cumberland 
and Northumberland, the Carboniferous sandstones, limestones and shales 
are well exposed, they present no continuation of either the plateau or puy- 
erup ions whmh play so prominent a part in the geology of Roxburghshire 
ml I umfnesshire. This deficiency is all the more noticeable seeing that 
of the N° ni G r0U r ? 8t ? m f exp0sed d0WU t0 its ver T base, in the deep dales 
e Noith of England. Had any truly interstratified volcanic material 
existed in the system there, it could hardly fail to have been detected. 
r 1 b 'f wh . contemporaneous volcanic rocks are absent, the northern 
Dig ish counties contain many intrusive masses of dolerite, diabase, andesite 
or other eruptive rocks, which may be found traversing all the subdivisions 
ol the Carboniferous system. These eruptive materials have taken two 
orms ; m some cases they rise as Dykes, in others they appear as Sills. 
. f( YKES, T7 Wltl1 re g ard to the dykes, some are probably much later than 
t ie Carboniferous period, aud consequently will he more appropriately con- 
sidered m Chapters xxxiv. and xxxv. The great Cleveland dyke, for example, 
\v rich runs across the Carboniferous, Permian, Triassic and Jurassic formations, 
is probably referable to the Older Tertiary volcanic period. One dyke known 
as the Hett Dyke, has been plausibly claimed as possibly of Carboniferous 
a ge. Tt runs in a W.S.W. direction from the Magnesian Limestone escarp- 
ment at Quarrington Hill, a few miles to the east of Durham, through 
t ie great Coal-field, across the Millstone Grit and Carboniferous limestone, 
disappearing near. Middleton in Teesdale. Its total length is thus about 
-fy miles. varies in breadth from about 6 to about 15 feet, aud appears 
to increase in dimensions as it goes westward. 1 
Sedgwiok ’ Tmns - Oeol. Soc. 2nd series, iii. part 1 (1826-28), p. 63 ; Trans. Cambridge Phil. Soc. 
U. (18^2), p. 21. Sir J. Lowthian Bell, Proc. Poy. Soc. xxiii. (1875), p. 543. 
