Ixiv REPORT — 1864. 



laid down on the Ordnance Map, the existence of which must be inferred from 

 the different levels at which the same formations crop out on the flanks of the 

 hills to the north and south of the city. I have therefore httle doubt that 

 the Bath springs, like most other thermal waters, mark the site of some great 

 convulsion and fracture which took place in the crust of the earth at some 

 former period — perhaps not a very remote one, geologically speaking. The 

 uppermost part of the rent through which the hot water rises is situated in 

 horizontal strata of Lias and Trias, 300 feet thick; and this may be more 

 modern than the lower part, which passes through the inclined and broken 

 strata of the subjacent coal-measures, which are unconformable to the Trias. 

 The nature and succession of these rocks penetrated by the Bath waters was 

 I first made out by the late "WiUiam Smith in 1817, when a shaft was sunk in 

 the vicinity in search for coal. The shock which opened a communication 

 through the upper rocks may have been of a much later date than that which 

 fractured the older and underlying strata ; for there is a tendency in the 

 earth's crust to jdeld most readily along hues of ancient fracture, which con- 

 stitute the points of least resistance to a force acting from below. 



If we adopt the theory already alluded to, that the nitrogen is derived 

 from the deoxidation of atmospheric air carried down by rain-water, we 

 may imagine the supply of this water to be furnished by some mountainous 

 region, possibly a distant one, and that it descends through rents or porous 

 rocks tiU it encounters some mass of heated matter by which it is converted 

 into steam, and then driven upwards through a fissure. In its downward 

 passage the water may derive its sulphate of lime, chloride of calcium, and 

 other substances from the decomposition of the gypseous, saline, calcareous, 

 and other constituents of the rocks which it permeates. The greater part of 

 the ingredients are common to sea-water, and might suggest the theory of a 

 marine origin ; but the analysis of the Bath springs by Merck and Galloway 

 shows that the relative proportion of the solid matter is far from agreeing 

 with that of the sea, the chloride of magnesium being absolutely in excess, that 

 is, 14 grains of it per gallon for 12 of common salt ; whereas in sea-water 

 there are 27 grains of salt, or chloride of sodium, to 4 of the chloride of mag- 

 nesium. That some mineral springs, however, may derive an inexhaustible 

 supply, through rents and porous rocks, from the leaky bed of the ocean, is 

 by no means an unreasonable theory, especially if we believe that the con- 

 tiguity of nearly all the active volcanos to the sea is connected with the 

 access of salt water to the subterranean foci of volcanic heat. 



Professor Roscoe, of Manchester, has been lately engaged in making a 

 careful analysis of the Bath waters, and has discovered in them three metals 

 which they were not previously known to contain — namely copper, stron- 

 tium, and lithium ; but he has searched in vain for caesium and rubidium, 

 those new metals, the existence of which has been revealed to us in the 

 course of the last few years by what is called spectrum analysis. By this 

 new method the presence of infinitesimal quantities, such as would have 

 wholly escaped detection by ordinaiy tests, are made known to the eye by 

 the agency of light. Thus, for example, a solid substance such as the 

 residue obtained by evaporation from a mineral water is introduced on a 

 platinum wii'e into a colourless gas-flame. The substance thus volatilized 

 imparts its colour to the flame, and the light, being then made to pass 

 through a prism, is viewed through a small telescope or spectroscope, as it is 

 called, by the aid of which one or more bright lines or bands are seen in the 

 spectrum, which, according to their position, number, and colour, indicate the 

 presence of different elementary bodies. 



