ADDRESS. Ixiii 



by hydrostatic pressure. This theory has been very generally adopted, as best 

 accounting for the constant disengagement of large bodies of nitrogen, even 

 where the rocks through which the spriug rises are crystalline and unfossili- 

 ferous. It %vill, however, of coiirse be admitted, as Professor Bischoff has 

 pointed out, that in some places organic matter has supplied a large part 

 of the nitrogen evolved. 



Carbonic-acid gas is another of the volatilized substances discharged by 

 the Bath waters. Dr. Gustav Bischoff, in the new edition of his valuable 

 work on chemical and physical geology, when speaking of the exhalations 

 of this gas, remarks that they are of universal occurrence, and that they 

 originate at great depths, becoming more abundant the deeper we penetrate. 

 He also observes that, when the silicates which enter so largely into the 

 composition of the oldest rocks are percolated by this gas, they must be con- 

 tinually decomposed, and the carbonates formed by the new combinations 

 thence arising must often augment the volume of the altered rocks. This 

 increase of bulk, he says, must sometimes give rise to a mechanical force of 

 expansion capable of uplifting the incumbent crust of the earth ; and the 

 same force may act laterally so as to compress, dislocate, and tilt the strata 

 on each side of a mass in which the new chemical changes are developed. 

 The calciilations made by this eminent German chemist of the exact amount 

 of distention which the origin of new mineral products may cause, by adding 

 to the volume of the rocks, deserve the attention of geologists, as affording 

 them aid in explaining those reiterated oscillations of level — those risings 

 and sinkings of land — which have occurred on so grand a scale at successive 

 periods of the past. There are probably many distinct causes of such 

 upward, downward, and lateral movements, and any new suggestion on this 

 head is most welcome ; but I believe the expansion and contraction of solid 

 rocks, when they are alternately heated and cooled, and the fusion and sub- 

 sequent consolidation of mineral masses, will continue to rank, as heretofore, 

 as the most influential causes of such movements. 



The temperature of the Bath waters varies in the different springs 

 from 117° to 120° F. This, as before stated, is exceptionally high, when we 

 duly allow for the great distance of Bath from the nearest region of active 

 or recently extinct volcanos and of violent earthquakes. The hot springs of 

 Aix-la-Chapelle have a much higher temperature, viz. 135° F., but they are 

 situated within forty miles of those cones and lava-streams of the Eifel 

 which, though they may have spent their force ages before the earliest 

 records of history, belong, nevertheless, to the most modern geological period. 

 Bath is about 400 miles distant from the same part of Germany, and 440 from 

 Auvergne — another volcanic region, the latest eruptions of which were geolo- 

 gically coeval Avith those of the Eifel. When these two regions in France 

 and Germany were the theatres of frequent convulsions, we may well suppose 

 that England was often more rudely shaken than now ; and such shocks as 

 that of October last, the sound and rocking motion of which caused so great 

 a sensation as it traversed the southern part of the island, and seems to have 

 been particularly violent in Herefordshire, may be only a languid reminder 

 to us of a force of which the energy has been gradually dying oiit. 



If you consult the geological map of the environs of this city, coloured by 

 the Government surveyors, you will perceive that numerous lines of fault or 

 displacement of the rocks are there laid down, and one of these has shifted 

 the strata vertically as much as 200 feet. Mr. Charles Moore pointed oiit to 

 me last spring, when I had the advantage of examining the geology of this 

 district under his guidance, that there are other lines of displacement not yet 



