110 EXPLANATION OF PLATE 69. 



Plate 69. V. I. p. 422. 



Fig. 1. Theoretical section, illustrating the Hydraulic 

 conditions of strata disposed in the form of Basins. 

 See Vol. I. p. 422, Note. (Original.) 



Fig. 2. Theoretical section, showing the effect of Faults, 

 and Dikes on water percolating inclined and per- 

 meable Strata. See Vol. I. p. 423, Note. (Original.) 



Fig. 3. Double Artesian Fountain at St. Ouen, near 

 Paris, raising water to supply a Canal basin, from 

 two strata at different depths. The water from 

 the lowest stratum rises to the greatest height. See 

 V. I. p. 423. Note. (Hericart de Thury.) 



and West veins, and near the rocks to which they were determined by 

 the electric currents." 



Tn a Letter to the Author upon this subject (June 29, 1836,) Mr. 

 Fox further remarks. 



" It should be observed that in proportion as the deposition of the 

 metals proceeded, the voltaic action must necessarily have been con- 

 siderably augmented, so as to render it highly probable that the metals 

 were chiefly deposited at rather an early period in the history of the 

 containing veins ; and their intersection by other veins seems to 

 strengthen this probability." 



Mr. Fox has found by experiment that when a solution of muriate 

 of Tin is placed in the voltaic current, a portion of the metal is de- 

 termined towards the negative pole, whilst another portion in the 

 state of an oxide passes to the positive pole. This fact appears to him 

 to afford a striking illustration of the manner in which Tin and Copper 

 have been separated from each other in the same vein, or in contiguous 

 veins, whilst these metals also very commonly occur together in the 

 same vein. 



