156 ECONOMICAL MINERALOGY. 



1 . Their general distribution. 



2. Their emergence from various rock formations, without regard to their relative age or 

 composition. 



3. The vast quantity of this sulphuretted water, and of the gas evolved. 



4. The uniformity and permanency of their composition and temperature. 



5. The fact that almost all these springs have a temperature somewhat above that of the 

 locality in which they exist, and that they may hence be fairly ranked in the class of thermal 

 springs. 



It is believed that the above facts cannot be satisfactorily explained without calling in the 

 aid of some powerful, deep-seated and widely extended agency. A modification or extension 

 of the chemical theory of volcanic action first proposed by Davy, and afterwards adopted and 

 strenuously advocated by Prof. Daubeny, will, in my opinion, fulfil the conditions which a 

 complete explanation requires. It is well known that this theory is founded upon the assumpr 

 tion that there exist in the interior of the earth vast quantities of the metallic bases of the 

 alkalies and alkaline earths ; that to these bases water is admitted, and, by its decomposition, 

 a necessary consequence of such an admission, (at least in the case of many of these bases,) 

 intense heat is produced, accompanied with vivid inflammation and the violent ejection of the 

 various products thus formed. If we extend this admission to the existence of sulphur, or of 

 the sulphurets of these metals, the presence and the action of water will give all the conditions 

 which we require. In this way, we can readily account for the gaseous and solid matters 

 which sulphur springs contain ; for the wide extent of country over which they occur, and the 

 other circumstances which characterize them ; and also for what no other theory seems so 

 well to explain, viz. the separate evolution of the gas tlurough the water, the existence of the 

 sulphates of lime, soda, etc., and the almost entire absence of sulphate of iron. 



In conclusion, I will only add, that although it becomes us to speak with caution in regard 

 to views of this kind, it is not easy to resist the conviction that the occurrence of our sulphu- 

 reous springs, at least, must be ascribed to some general cause ; and that Uke volcanoes, they 

 are the outward exhibitions of the great volcanic focus, whether that is brought into operation 

 by mechanical or chemical agencies. 



PETRIFYING SPRINGS. 



The history of petrifying springs affords a fine illustration of the intimate relations which 

 exist between the researches of the chemist and geologist ; for whatever difference of opinion 

 may prevail concerning the true theory of the petrifying process which in many situations is 

 daily going on, there is no doubt of the general fact that chemical agencies are largely con- 

 cerned in it. 



The explanation ordinarily given of the formation of travertin or calcareous tufa, stalactites, 

 etc., is sufficiently simple, and may be easily comprehended. The water in certain springs 

 holds in solution considerable quantities of carbonate and sulphate of lime, and occasionally 

 of silica, which are deposited when the water comes into contact with the air. This process 



