ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 173 



In the thermal springs, although the solid contents vary 

 very greatly, the lowest amount is 84 grains per gallon, while 

 the average is 685 grains. In the phreatic springs the lowest 

 amount was 13-59 grains, the highest 46-97 grains or not much 

 more than half the lowest of the thermals, while the average was 

 only 29-44 grains. 



The following substances were found in greater or less pro- 

 portion in the thermals, viz. — the gases oxygen, nitrogen, and 

 carbonic acid ; sulphuric, nitric, carbonic and silicic acids, 

 chlorine, bromine, and iodine, in combination with the following 

 bases, viz. — ammonia, soda, potassa, lithia, csesia, rubidia, lime, 

 magnesia, alumina, iron, manganese, copper All the above, 

 except bromine, iodine, ceesia and rubidia, were also found in 

 the phreatic waters; and in the greatly modified phreatic water 

 of Dolcoath arsenic was also found.* 



The analyses of thermal waters by Dr. Miller and Mr. 

 Phillips, which are quoted above, shew that the first four of 

 those included in Table 1 are essentially diluted sea water, 

 somewhat modified in passing through the rocks, f the dilution 

 of course being occasioned by access of surface waters. 



Fig. 12, Plate ix, taken from Mr. Phillips's paper already 

 quoted, I illustrates one of the many modes by which sea water 

 after penetrating to great depths through fissures, can make its 

 way into the workings of a mine as a spring. This may be regarded 

 as an example of ''canalicular" circulation. Other springs 

 have been noticed in North Poskear, North Crofty, and many 



* Further particulars of these springs with full analyses will be found as 

 follows. 



W. W. Smyth (for W. A. Miller, M.D.) British Assoc. Bath Meeting, 1864. 



H. Tilly. Particulars of a thermal spring at Wheal Seton. Report M. A. 

 for 1872, p. 53. 



J. A. Phillips. Phil. Mag. July, 1873, and March, 1874. 



f The most notable modification seems to be that both at Wheal Seton and 

 Wheal Clifford lithia had been taken up from the granite through which the 

 water must have made its way (and in the case of Wheal Clifford csesia and 

 rubidia also) ; and at Wheal Seton and Botallack the water besides being diluted — 

 presumably with fresh water percolating from the surface — has lost its magnesia 

 to a great extent, while the rocks passed through are more highly magnesian than 

 usual — facts bearing very materially upon the theory of serpentinization. See 

 Phillips, Q.J.G. Soc, 123, p. 319, and T. Sterry Hunt, Origin of Serpentine. 



:l:Phil. Mag., July, 1873, 



