CHAP. XXIX 
THE ISLE OF MAN 
23 
recognition of true intercalated volcanic rocks among the calcareous 
formations of the southern end of the island. These rocks have subse- 
quently been studied in greater detail by a number of geologists. An 
excellent general account of them was published in 1874 by Mr. John 
Horne, of the Geological Survey. 1 A few years later some further obser- 
v a tions on them were prepared by J. Clifton Ward.' More recently 
their petrography has been studied by Messrs. E. Dickson, P. Holland and 
F - Hutley, 3 and in more detail by Mr. B. Hobson. 4 To some of the 
observations of these writers reference will be made in the succeeding 
pages. During the progress of the Geological Survey in the Isle of Man, 
the rocks in question have been mapped in detail by Mr. A. Strahan 
and Mr. G. W. Lamplugh, and I have had an opportunity of examining 
the coast-sections with the last-named geologist. The following description 
°f these sections is taken mainly from my field note-book. The full details 
w 'fl a ppear in the official Memoirs. 
It may he remarked at the outset that the last outcrop of the plateau- 
lavas of the Solway basin occurs only 60 miles from the south end of the 
Isle of Man, at the foot of the hills of Galloway, the blue outline of which 
can he seen from that island. The distance from the Manx volcanoes to 
l he nearest of the puys of Liddesdale is about 100 miles. Though the 
fragment which has been left of the ejections is too small to warrant any 
confident parallelism, there appears to be reason to believe that, alike m 
geological age and in manner of activity, the Manx volcanoes may he 
classed with the type of the puys. 
The Carboniferous strata of the Isle of Man lie in a small trough at 
the south end of the island. The lowest members of the series consist of 
red conglomerates and sandstones, which pass upward into dark limestones 
full of the characteristic fossils of the Carboniferous Limestone. As the 
bottom of the basin is on the whole inclined seawards, the highest strata 
occur along the extreme southern coast. . It is there that the volcanic 
rocks are displayed. They occupy a narrow strip less than two miles 111 
length, which is almost entirely confined to the range of cliffs and the 
ledges of the foreshore. Yet though thus extremely limited in area, they 
have been so admirably dissected along the coast, that they furnish a 
singularly ample body “of evidence bearing on the history of Carbon- 
iferous volcanic action. 
Unfortunately the bottom of the volcanic group is nowhere visible. At 
Hie east or lower end of the series, exposed on the shore, an agglomerate 
w ith its dykes appears to truncate the Castletown Limestones. No trace 
of any tuff has been noticed among these lower limestones. We may infer 
that the volcanic activity began after they were deposited. The highest 
accessible portions of the volcanic group, as Mr. Horne showed, are clearly 
3 Jrans - Gfcol. Soc. Edin. ii. (1874), p, 332. 
Proc. Liverpool Geol. Soc. vol. vi. (1888-89), p. 123. 
3 Geol. Mag. 1880, p. 4. 
Quart. Journ. Geol. Soc. xlvii. '(1891), p. 432. Tins paper was reprinted with additions 
UUc Corr ections in Yn Liocir Manninagh , Douglas, Isle of Man, vol. i. No. 10, pn 
