Economic Geology. 29 



primary rocks, admitting of the inference that the chain of 

 hills itself was formed of members of this series, there can be 

 but little hesitation in replying in the negative. We cannot 

 of course say with absolute certainty that the conglomerate 

 is underlaid by the solid rock, but from the considerations 

 adverted to, the probabilities are in favour of its being so. 

 But although in the instance of the boring operations in 

 Fort William it appears probable that success never would 

 have been attained, it by no means follows that deltas gene- 

 rally are ill calculated for similar experiments. On the 

 contrary, these operations, by exhibiting undoubted proofs of 

 changes in the relative levels of the part of deltas due to the 

 action of disturbing forces, continued at intervals during the 

 deposition of their constituent beds, furnish good grounds 

 for the belief that the hydraulic arrangements required for 

 the success of the Artesian system exist in such formations, 

 and that attempts to establish overflowing wells by boring 

 through them, may be made without involving any violation 

 of the general principles already developed on which the ac- 

 tion of these depends. 



Sufficient has now it is hoped been said to convey a gene- 

 ral impression of the geological relations on which the Arte- 

 sian method is essentially dependant, but it remains still to 

 notice the principal sources of failure to which it is subject, 

 an acquaintance with these being absolutely necessary to the 

 formation of a correct estimate of the propriety of boring in 

 any given locality. 



The effect of those disturbing forces to which geologists 

 have by almost common consent assigned an igneous origin, 

 and which have prevailed during every epoch, has been the 

 production of innumerable dislocations in the strata of which 

 the earth's crust is composed, and we accordingly find them 

 fractured, altered, and upheaved in every possible way. Se- 

 condary and tertiary equally with transition and primary 

 rocks have felt the influence of these disruptive agents, and 

 the continuity which is so essential to the hydraulic effici- 



