Sir C. Lyell on the Mineral Waters of Bath. 23 
If, therefore, large bodies of hot water permeate mountain-masses 
at great depths, they may in the course of ages superinduce in 
them a crystalline structure; and in some cases strata in a lower 
position and of older date may be comparatively unaltered, re- 
taining their fossil remains undefaced, while newer rocks are 
rendered metamorphic. This may happen where the waters, 
after passing upward for thousands of feet, meet with some ob- 
struction, as in the case of the Wheal-Clifford spring, causing 
the same to be laterally diverted so as to percolate the surround- 
ing rocks. The efficacy of such hydro-thermal action has been 
admirably lilustrated of late years by the experiments and obser- 
vations of Sénarmont, Daubrée, Delesse, Scheerer, Sorby, Sterry 
Hunt, and others. 
he changes which Daubrée has shown to have been produced 
by the alkaline waters of Plombiéres, in the Vosges, are more 
especially instructive. These thermal waters have a temperature 
of 160° F., and were conveyed by the Romans to baths through 
long conduits or aqueducts. The foundations of some of their 
works consisted of a bed of concrete, made of lime, fragments 
of brick and sandstone. Through this and other masonry the 
hot waters have been percolating for centuries, and have given 
rise to various zeolites—apophyllite and chabazite besides others ; 
also to calcareous spar, aragonite, and fluor spar, together with 
siliceous minerals, such as opal,—all found in the interspaces of 
the bricks and mortar, or constituting part of their rearranged 
materials, The quantity of heat brought into action in this in- 
stance in the course of 2000 years has, no doubt, been enormous, 
although the intensity of it developed at any one moment has 
been always inconsiderable. : 
The study, of late years, of the constituent parts of granite 
has in like manner led to the conclusion that their consolidation 
has taken place at temperatures far below those formerly suppo- 
sed to be indispensable. Gustav Rose has pointed out that the 
quartz of granite has the specific gravity of 2:6, which charae- 
terizes silica when it is precipitated from a liquid solvent, and 
not that inferior density, namely 23, which belongs to it when 
it cools and solidifies in the dry way from a state of fusion. 
ut some geologists, when made aware of the intervention on 
a large scale, of water, in the formation of the component min- 
erals of the granitic and volcanic rocks, appear of late years to 
ave been too much disposed to dispense with intense heat when 
accounting for the formation of the erystalline and unstratified 
‘rocks. As water ina state of solid combination enters largely 
into the aluminous and some other minerals, and therefore plays 
no small part in the composition of the earth’s crust, it follows 
t, when rocks are melted, water must be present, indepen- 
dently of the supplies of rain-water and sea-water which find 
