16 Sir C. Lyell on the Mineral Waters of Bath. 
should soon see a considerable cone built up, with a crater inthe 
middle; and if the action of the spring were intermittent, 80 3 
that ten or twenty years ree elapse between the periods when 4 
solid matter was emitted, or (say) an interval of three centuries, 
as in the case of Vesuvius hereaee 1806 and 1681, the discharge | 
would be on so grand a scale as to afford no mean n objec of com- — 
parison with the intermittent outpourings of a v 4 
Dr. Daubeny, after devoting a month to the easial of the — 
Bath waters, in 1833, ascertained that the daily evolution of ni- — 
trogen gas ¢ amounted to no less than 250 cubic feet in volume. _ 
This gas, he remarks, is not only characteristic of hot springs, — 
but is largely disengaged from volcanic craters during eruptions. — 
In both cases, he suggests that the nitrogen may be derived from , 
Sah whe air, which is always dissolved in rain- water, and — 
Ww 1en this water penetrates the Hone s crust, must be car- E 
static 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 spring 4 
rises are crystalline and unfossiliferous. It will, however, of | 
course be admitted, as Professor Bischof has pasar out, that 
in some places sage matter has supplied a large part of the : 
nitrogen evolve : 
Carbonic seid vas is another of the volatilized substances dis- 4 
charged by the Bath waters. Dr. Gustav Bischof, 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 4 
meets, becoming more abundant the dee eeper we penetrate. He | 
also observes that, when the silicates which enter so largely into — 
the composition of the oldest rocks are percolated by ae gas, 5 
they must be continually decomposed, and the 
by the new combinations thence arising must obi mean the 3 
volume of the —— rocks. Lo increase of bulk, he 4 7 
must sometimes give rise to a mechanical force of arth; and the q 
pable of oe the Rapenibest crust of the eart the ] 
same force may act laterally, so as to compress, dislocate, a: a 
e strata on each side of a mass in which the . chemical q 
aents are developed. _ calculations made by this eminent _ 
