740 PLUTONIC ACTION. [Ch. XXXV. 



remarkable uniformity of temperature from century to century. A 

 like uniformity is also persistent in the nature of the earthy, metallic, 

 and gaseous substances with which they are impregnated. It is well 

 ascertained that springs, whether hot or cold, charged with carbonic 

 acid, and especially with hydrofluoric acid, which is often present in 

 small quantities, are powerful causes of decomposition and chemical 

 reaction in rocks through which they percolate. 



The changes which Daubree has shown to have been produced by 

 the alkaline waters of Plombieres in the Yosges, are more especially 

 instructive.* These waters have a heat of 160° F., or an excess of 

 109° above the average temperature of ordinary springs in that district. 

 They 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 among others ; also to calcareous spar, arragonite, 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 instance in the course of 2000 years has, no doubt, been enormous, 

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

 inconsiderable. 



From these facts and from the experiments and observations of 

 Senarmont, Daubree, Delesse, Scheerer, Sorby, Sterry, Hunt, and others, 

 we are led to infer that when in the bowels of the earth there are large 

 volumes of molten matter, containing heated water and various acids 

 under enormous pressure, these subterranean fluid masses will gradually 

 part with their heat by the escape of steam and various gases through 

 fissures, producing hot springs ; or by the passage of the same through 

 the pores of the overlying and injected rocks. Even the most compact 

 rocks may be regarded, before they have been exposed to the air and 

 dried, in the light of sponges filled with water. According to the 

 experiments of Henry, water, under an hydrostatic pressure of 96 feet, 

 will absorb three times as much carbonic acid gas as it can under the 

 ordinary pressure of the atmosphere. There are other gases, as well 

 as the carbonic acid, which water absorbs, and more rapidly in pro- 

 portion to the amount of pressure. Although the gaseous matter first 

 absorbed would soon be condensed, and part with its heat, yet the 

 continual arrival of fresh supplies from below might, in the course of 

 ages, cause the temperature of the water, and with it that of the con- 

 taining rock, to be materially raised, the water acts not only as a vehicle 

 of heat, but also by its affinity for various silicates, which, when some 

 of the materials of the invaded rocks are decomposed, form quartz, 

 felspar, mica, and other minerals. As for quartz, it can be produced 



* Daubree, Sur le Metamorpkisme ; Paris, 1860. 



