32 
VOLCANIC PRODUCTS 
BOOK I 
error in such cases may here be pointed out. In the first place, where 
angular detritus has been precipitated into still w'ater, as, lor instance, 
from a crag or rocky declivity into a lake, a very coarse and tumultuous 
l^-ind of breccia may be formed. It is conceivalde that, in course of 
time, such a breccia may be buried under ordinary sediments, and may 
thereby be preserved, while all trace of its parent precipice may have 
disappeared. The breccia might resemble some true volcanic agglomerates, 
but the resemblance would be entirely deceptive. 
In the second place, notice must be taken of the frequent results of 
movements within the terrestrial crust, whereby rocks have not only been 
ruptured but, as already pointed out, have been crushed into fragments. 
In this way, important masses of breccia or conglomerate have been formed, 
sometimes running for a number of miles and attaining a breadth of several 
hundred feet. The stones, often in huge blocks, have been derived from 
the surrounding rocks, and while sometimes angular, are sometimes well- 
rounded. They are imbedded in a finer matrix of the same material, and 
may be scattered promiscuously through the mass, in such a way as to 
present the closest resemblance to true volcanic breccia. Where the 
crushed material has included ancient igneous rocks it might deceive even 
an experienced geologist. Indeed, some rocks w’hich have been mapped and 
described as volcanic tuffs or agglomerates are now known to be only 
examples of “ crush-conglomerates.” ^ 
Not only have vast quantities of detritus of non-volcanic rocks been 
sliot forth from volcanic vents, but sometimes enormous solid masses of 
rock have been brought up by ascending lavas or have been ejected by ex- 
plosive vapours. .Every visitor to the puys of Auvergne will remember the 
oreat cliff-like prominence of granite and mica-schist which, as described long 
ago by Scrope, lias been carried up by the trachyte of the I’uy Chopine, 
and forms one of the summits of the dome (Fig. 344). The same pheno- 
menon is observable at the Euy de Montchar, wdiere large blocks of gianite 
have been transported from the underlying platform. Abich has descriljed 
some remarkable examples in the region of Erzeroum. The huge crater ot 
Palandokiin, 9687 feet above the sea contains, in cliff-like projections from 
its walls as well as scattered over its uneven bottom, great masses of 
marmorised limestone and alabaster, associated with pieces of the green 
chloritic schists, serpentines and gabl.u'os of the underlying non-volcanic 
platform. These rocks, wdiich form an integral part of the structure of the 
crater, have been carried up by masses of trachydoleritic, andesitic and 
quartz-trachytic lavas.'^ Examples will be given in a later chapter showing- 
how gigantic blocks of mica-schist and other rocks have been carried man} 
hundred feet irpwnrds and buried among sheets of lava or masses of agglo- 
merates dui’ing the Tertiary volcanic period in liritaiir (iig. 262). 
' For an account of “ crush -conglomerates, ” sec Mr. Lainplngli’s paper on those of the Isle of 
Man, Quart. Journ. <leol. Soc., 11. (189.5), p. 563. Mr. M ‘Henry has pointed to probable cases of 
mistake of this kind in Ireland, Natii.ir, 5th March 1896. A. Gcikie, Gcol. Mag. November 1896. 
2 Abich, Geologic des Armmwclien Moch/cmdcs (Part ii., -vvestern hall'), 1882, p. 76. 
