30 KEMPS ORE DEPOSITS. 



waters, all of which have descended from the surface, and that the 

 metals have been gathered up from a disseminated condition in rocks, 

 igneous, sedimentary, and metamorphic, no more definite state- 

 ment is possible. This theory is of necessity largely speculative, 

 because the materials for its verification are beyond actual inves- 

 tigation. 



1.04.05. In favor of lateral secretion the following arguments 

 may be advanced. I. According to Sandberger, actual experience 

 with the conduits, either natural or artificial, of mineral springs, 

 shows that a deposit seldom, if ever, gathers in a moving current. 

 It is only when solutions come to rest on the surface and are 

 exposed to oxidation and evaporation that precipitation ensues. 

 Deposits in veins have therefore formed in standing waters, whose 

 slight overflow or evaporation would be best compensated by the 

 equally slight and gradual inflow from the walls. If in hot springs 

 there were a strong and continuous flow from below and discharge 

 from above, the mineral matter would reach the surface. (Sand- 

 berger, Untersuchungen uber Erzgange, Heft I.) Hence the deposit 

 would be more likely to gather by the slow infiltrations from the 

 wall rock, which would stand in cavities like a well. We have, 

 however, some striking instances of deposits in artificial con- 

 duits. 



Prof. H. S. Munroe has called the writer's attention to a case 

 recently met by him. The fourteen-inch column pipe of a pump 

 at the Indian Ridge Colliery, Shenandoah, Penn., which was rais- 

 ing ferruginous waters, became reduced in diameter to five inches 

 within two years by the deposit of limonite. The same amount 

 of water was forced through the five-inch as through the fourteen- 

 inch. By figuring out the stroke and cylinder contents, it was 

 found that in the clear pipe the water moved 162 feet per minute, 

 and in the contracted pipe 1268 feet. And yet the deposit gath- 

 ered. The conditions necessitated the continuous action of the 

 pump, and it was not idle over two hours in each two months 

 of that period. The boiler feed-pipes of steamers plying on the 

 Great Lakes also become coated with salts of lime. Years ago a 

 disastrous boiler explosion occurred from the virtual stoppage of 

 the feed by this precipitation. 



1.04.06. II. If a vein were opened up, in mining, which ran 

 through two different kinds of rock, and if in the one rock one 

 kind of ore and gangue minerals were found, and in the other a 

 different set, the wall rock would clearly have some influence. 



