GAGE IRON ORES IN MISSOURI. 183 



nor by injection could, foi- example, the ore-deposit on Pilot 

 Knob have been formed ; neither by infiltration, if the material 

 deposited was necessarily introduced in a state of aqueous solu- 

 tion from below : but if we interpret Infiltration to mean that a 

 solvent passes through the enclosing rock to the fissures, and may 

 either before reaching the rock hold in solution the material to be 

 deposited or dissolve the particles on its passage — but geograpJii- 

 cally the source of the solvent is beloTV the point where the depo- 

 sition is made — then the Infiltration of the Ascension Theory 

 resolves itself into the Lateral-secretion Theory, and they become 

 one and the same. It is only by the process of lateral-secretion I 

 can account for many of the ore-deposits in the Porphyries ; for 

 example, in the-Pilot Knob formation this seems to me the only 

 tenable theory. For we have in Pilot Knob a large iron-ore bed 

 lying in Porphyry : we cannot account for it havftig been depos- 

 ited directly from water ; for we would have to imagine first a 

 bed of Porphyry, then a large body of water holding the material 

 in solution, then a precipitation, and afterwards a porphyritic 

 mass formed on top of the ore-bed. And where shall we look 

 for the origin of this Porphyry? Echo must answer, Where.'* 

 for science certainly will not. It cannot be accounted for by 

 Sublimation, for fissures were necessary for the reception of the 

 sublimated material, and also as channels for conduction ; the 

 bed is not a fissure caused by contraction or some other force 

 of nature, and, if it were, no trace of fissures exists below through 

 which the material could have been conveyed to the existing bed. 



The same reasons can be urged against Injection, the deposition 

 of the bed is too regular to be the repository of injected matter ; 

 and if the ore had been injected into its present position, traces of 

 veins or fissures would exist in the underlying Porphyry, but no 

 such traces exist. Consequently all these theories are untenable, 

 and for a solution of the problem as to the origin of ore-deposits 

 we only have the Lateral-secretion Theoiy, but which, I think, is 

 all that is necessary for an explanation. 



When I first examined the ore-deposit on Pilot Knob, I was at 

 a loss to account for its origin ; the conglomeratic porphyry mass 

 overlying the ore-bed forbid the thought of the ore having been 

 precipitated directly from a large body of water which had pre- 

 viously held the ore in solution. And, for reasons previously 

 stated, an igneous origin was equally untenable : the formation 

 on Cedar Mountain originated the germ of the thought, which 



