274: ANNUAL OF SCIENTIFIC DISCOVERY. 



behind long before the spring reaches the earth's surface. If this 

 theory be adopted, it will follow that the metalliferous portion of a 

 fissure, originally thousands of feet or fathoms deep, will never be ex- 

 posed in regions accessible to the miner until it has been upheaved by 

 a long series of convulsions, and until the higher parts of the same rent, 

 together with its contents and the rocks which it had traversed have 

 been removed by aqueous denudation. Ages before such changes are 

 accomplished, thermal and mineral springs will have ceased to act : so 

 that the want of identity between the mineral ingredients of hot springs 

 and the contents of metalliferous veins, instead of militating against 

 their intimate relationship, is in favor of both being the complemen- 

 tary results of one and the same natural operation. 



Metamorphism of the Sedimentary Rocks. But there are other char- 

 acters in the structure of the earth's crust more mysterious in their 

 nature than the phenomena of metalliferous veins, on which the study 

 of hot springs has thrown light. I allude to the metamorphism of 

 sedimentary rocks. Strata of various ages, many of them once full of 

 organic remains, have been rendered partially or wholly crystalline. 

 It "is admitted on all hands that heat has been instrumental in bringing 

 about this rearrangement of particles, which, when the metamorphism 

 has been carried out to its fullest extent, obliterates all trace of the 

 imbedded fossils. But as mountain-masses many miles in length and 

 breadth, and several thousands of feet in hight, have undergone such 

 alteration, it has always been difficult to explain in what manner an 

 amount of heat capable of so entirely changing the molecular condition 

 of sedimentary masses could have come into play without utterly an- 

 nihilating every sign of stratification, as well as of organic structure. 

 Various experiments have led to the conclusion that the minerals 

 which enter most largely into the composition of the metamorphic 

 rocks have not been formed by crystallizing from a state of fusion, or 

 in the dry way, but that they have been derived from liquid solutions, 

 or in the wet Avay, a process requiring a far less intense degree of heat. 

 Thermal springs, charged w-itli carbonic acid and with hydro-fluoric 

 acid (which last is often present in small quantities), are powerful 

 causes of decomposition and chemical reaction in rocks through which 

 they percolate. If, therefore, large bodies of hot water permeate 

 mountain-masses at great depths, they may, in the course of ages, su- 

 perinduce in them a crystalline structure ; and, in some cases, strata 

 in a lower position and of older date may be comparatively unaltered, 

 retaining their fossil remains undefaced, while newer rocks are ren- 

 dered metamorphic. This may happen where the waters, after passing 

 upwards for thousands of feet, meet witli some obstruction, as in the 

 case of the Wheel-Clifford spring, causing the same to be Literally 

 diverted so as to percolate the surrounding rocks. The efficacy of 

 such hydro-thermal action has been admirably illustrated of late years 

 by the experiments and observations of Senarmont, Daubree, Delesse, 

 Scheerer, Sorby, Sterry Hunt, and others. 



The changes which Daubree has shown to have been produced by 

 the alkaline waters of Plombieret, 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 



