26 o 
THE DEVONIAN VOLCANOES 
BOOK V 
inasmuch as it would, seem to have heen deposited in beds among con- 
temporaneous -rocks of the former description by the agency of water, after 
having been ejected from fissures or craters in the shape of ashes and 
cinders, precisely as we may now expect would happen with the ashes and 
cinders ejected from volcanoes, particularly insular and littoral volcanoes, 
into tlie sead Again he speaks of “ two kinds of trappean rocks having 
probably heen erupted, one in the state of igneous fusion, and the other in 
that of ash, during the time tliat the mud, now forming slates, was deposited, 
tlie mixtures of volcanic and sedimentary materials being irregular from the 
irregular action of the respective causes whicli produced them ; so that thougli 
the one may have been derived from igneous action, and the other from 
the ordinary abrasion of pre-existing solid rocks, they were geologically con- 
temporaneous. " He recognized tlie origin of the amygdaloidal varieties of 
rock, and by dissolving out the caleite from their cells showed how close 
was their resemblance to modern pumice.® 
Since these early researches many geologists have studied tlie igneous 
rocks ot Devonshire. I would especially refer to the labours of Mr. 
Allport,* the late J. A. Phillips,*' Mr. Eutley,® the late Mr. Champer- 
iiowne,' Air. W. A. E. Ussher,® Mr. Hobson," and General MAIahon.**" Air. 
Champernowne in particular has shown the abundance of volcanic material 
among the rocks of Devonshire, and the resemblance which in this respect 
they ofier to the Devonian system of Horth Germany. 
Unfortnnately the geological structure of the PalcTozoic rocks of the 
South-west of England has been complicated to an amazing extent liy 
plication and fracture, with concomitant cleavage and metamorphism. 
Hence it is a task of extreme difficulty to trace out with any certainty 
definite stiatigraphical horizons, and to determine the range of contem- 
poraneous volcanic action. Air. Ussher has shown with what success this 
task may he accomplished when it is pursued on a ba.sis of minute mapping', 
combined with a sedulous collection and determination of fossils.^* But 
years must necessarily elapse before such detailed work is carried over the 
whole Devonian region, and probably not till then will the story of the 
volcanic history of the rocks he adequately made out. 
In the meantime, it has heen established that while there is a sincfular 
’ “Report on the Geology of Cornwall, Devon and West Somer.set,” Mem. Geol. Survei/, 
1839, p. .37. = Op. cit. p. o7. 3 pp. cit. pp. 57, 61. 
Qumi. Journ. Geol. Soc. xxxii. (1876), p. 418. 
° Op. cU. -xx.xi. (1875) p. 325, xxxii. (1876) p. 155, xxxiv. (1878) ]>. 471. 
'' “llrentTor,” Mem. Geol. Surv. p. 18; Quart. Journ. Geol. Soc. lii. (1896), p. 66. 
^ See in ijartioular his ha-st paper “On the Jl.shprington Volcanic Series of South Devon ’’ 
Quart. Journ. Geol. Soc. vol. xlv. (1889), p. 369. ’ 
^ * This geologist ha.s .spent many laboriou.s years in the investigation of the geolog}- of Devon- 
shire, and has published numerous iiapers on the subject, in the Transactions of the Devonshire 
Association and of the Jiopal Cornwall Geological Society, in the Proceedings of the Somersetshire 
Archmloyical and Natural History Society, and of the Geologists' Association, in the Geological 
Magazine, and the Quarterly Journal of the Geological Society. Reference may especially be made 
to hi.s Memoir in the last named journal, vol. xlvi. (1890), p. 487. 
^ Quart. Journ. Geol. Soc. xlviii. (1892), p. 496. 
Op. cit. xlix. (1893), p. 385. u .See Memoir cited in a previous note. 
