and the Nature of the Liquidity of Lavas. 195 
entangled ; and how (according to these experiments) it might 
flash into bubbles of vapour on the reduction of its temperature 
by exposure to the air. 
M. Deville, in his recent observations on the vapours disen- 
gaged from Vesuvius since the eruption of May in last year (for 
the perusal of which I am indebted to the kindness of my friend 
Dr. Daubeny), arrived at the conclusion, to use his own words, 
that ‘water in the proportion occasionally of 999 per mille must 
have formed an integral part of the Vesuvian lava at the moment 
of its emission; and, consequently, that in the interior of the 
incandescent lava there is such an arrangement of molecules as 
to permit the gaseous and volatile matters to remain there im- 
prisoned until, in the progress of cooling and consolidation, they 
evolve themselves.” 
Above all, M. Scheerer of Christiania, the eminent Norwegian 
geologist, who is better acquainted perhaps than any other with 
the granites of that country, published in 1847 a theory, which, 
he says, his observations had suggested to him in 1833, on the 
production of granite, entirely identical with that which I had 
ventured to suggest in 1824-25. I take the following account 
of it from the paper read before the Geological Society of France 
in 1847, and published in the fourth volume of the Bulletin de 
la Soc. Géol. p. 468. 
M. Scheerer attributes what he calls the “ plasticity” of gra- 
nite when protruded on or towards the surface of the earth (a 
condition evidenced by the veins it throws into the fissures of 
neighbouring rocks) to the combined action of water and heat. 
He describes the water as “intercalated between the solid atoms 
of the crystalline and other constituent minerals, endeavouring 
to escape by its tendency to vaporization, and consequent elas- 
ticity, but unable to do so owing to the pressure to which the 
enclosing mass is subject.”” He considers the water so contained 
in granite to be “ primitive ;” that is, one of the original bases 
of the rock, and not the result of infiltration. He attributes to 
it the solution of the quartz, aided by the alkali, and the con- 
sequent moulding of this mineral on the felspar-crystals. He 
even goes the length of styling the condition of granite before 
“ed protrusion by the term “une bouillie aqueuse,” a granitic 
oth. 
These theoretical opinions of M. Scheerer appear to have 
received the assent of M. Elie de Beaumont and other French 
geologists*. Their exact conformity with those which were first 
developed in my treatise on Volcanoes, published in 1824-25, 
and repeated in the Preface to my volume on Central France in 
* See Bulletin de la Soc. Géol. France, new series, vol. iv. p. 1312. 
O02 
