Ixviii REPORT — 1864 



trated of late years by the experiments and observations of Scnarmont, 

 Daubree, Delesse, Schcerer, Sorby, 8tcrry Hunt, aod others. 



The changes which Daubree lias shov.^u to have been produced by the 

 alkaline waters of Plombieres, in the Vosges, are more especially instructive. 

 These thermal waters have a temperature of 160° F., and were conveyed by 

 the llomans to Ijaths through long conduits or aqueducts. The foundations 

 of some of their works consisted of a bed of concrete made of lime, frag- 

 ments 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 among others ; also to calcareous spar, 

 arragonite, and iluor 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 

 instance in the course of 2000 years has, no doubt, been enormous, although 

 the intensity of it developed at any one moment has been always incon- 

 siderable. 



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 supposed to be indispensable. Gustav 

 Eose has pointed out that the quartz of granite has the specific gravity 

 of 2-6, which characteriz;cs silica when it is precipitated from a liquid 

 solvent, and not that inferior density, namely 2-3, which belongs to it when 

 it cools and solidifies in the dry way from a state of fusion. 



But some geologists, when made aware of the intervention on a large 

 scale, of water, in the formation of the component minerals of the granitic 

 and volcanic rocks, appear of late years to have been too much disposed to 

 dispense with intense heat when accounting for the formation of the crystal- 

 line and unstratified roclcs. As water in a state of solid combination enters 

 largely into the aluminous and some other minerals, and therefore plays no 

 smaU part in the composition of the earth's crust, it follows that, when rocks 

 are melted, water must be present, independently of the supplies of rain- 

 water and sea-water which find their way into the regions of siibterranean 

 heat. But the existence of water under great pressure affords no argument 

 against our attributing an excessively high temperature to the mass with 

 which it is mixed up. StiU less does the point to which the melted matter 

 must be cooled down before it consolidates or crystallizes into lava or granite 

 afford any test of the degree of heat which the same matter must have 

 acquired when it was melted and made to fonn lakes and seas in the interior 

 of the earth's crust. 



We learn from Bunsen's experiments on the Great Geyser in Iceland, that 

 at the depth of only seventy-four feet, at the bottom of the tube, a column of 

 water may be in a state of rest, and yet possess a heat of 120° Centigrade, or 

 248° F. What, then, may not the temperature of such water be at the depth 

 of a few thousand feet ? It might soon attain a white heat under pressure ; 

 and as to lava, they who have beheld it issue, as I did in 1858, from the 

 south-western flanks of Yesuvius, with a sm-face white and glowing like 

 that of the sun, and who have felt the scorching heat which it radiates, will 

 form a high conception of the intense temperature of the same lava at the 

 bottom of a vertical column several miles high, and communicating with a 

 great reservoir of fused matter, which, if it were to begin at once to cool 

 down, and were never to receive future accessions of heat, might require a 

 whole geological period before it solidified. Of such slow refrigeration hot 

 springs may be among the most effective instruments, abstracting slowly 



