ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 171 



There are few mining regions in wMcli thermal springs are 

 not known — although there is some reason to believe that cceteris 

 paribus they are less numerous, and their temperatures are lower, 

 in proportion to the antiquity of the deposits; — and even when 

 they occur in non-mining regions they are rarely devoid of 

 metallic constituents. 



It has been well said, that while mineral springs and solfa- 

 tara action are the remnants of volcanic disturbances, an ancient 

 mining region may be looked upon as exhibiting the roots of 

 such a region laid bare by denudation.*' 



Thermal springs are not unknown in the West of England, 

 although the denudation has been so great and the mineral 

 deposits are so ancient that their action may now be regarded as 

 almost extinct. 



Mr. J. A. Phillips, who had made a special study of the 

 relations of thermal springs to ore-deposits, stated some of his 

 conclusions thereon, in 1871, as follows, — maintaining the same 

 position also in his work on ore-deposits, published in 1884. 



1. Metalliferous lodes are more numerous and more pro- 

 ductive near igneous rocks than elsewhere. 



2. There have been volcanic eruptions at all periods of the 

 earth's history (so far as we can read that history in 

 the stratified rocks). 



3. Solfatara action and thermal springs are often the latest 



active evidences of volcanic disturbance. 



4. Crystalline quartz, iron pyrites, and other minerals are 

 now being deposited in veins having many of the 

 characters of ordinary lodes, by solfatara action (as at 

 the Steamboat Springs in Nevada). f 



The connexion between thermal springs and metalliferous 

 veins is discussed in considerable detail by Mr. Phillips in 

 subsequent papers to that before quoted — and he also refers to 

 a recently formed quartz deposit containing silver, which had 

 been previously described by my friend Dr. Oxland of Plymouth. J 



*" Mineral veins seem to be the roots of mineral springs " Sollas, discussion 

 on Foster's paper on the great flat lode, Q. J. G-. Soc. 



fSee Phil. Mag., Dec. 1871, Origin of Mineral Veins. I 



JSee J. A. PhilUps, Phil. Mag., Nov., 1878. 



