ORIGIN OF THE OXIDES OF IRON. 97 



ore at the south. The former belong to a modern period comparatively, while the latter is 

 very ancient. Still, the facts that the masses at the north exist, and have been so remarkably 

 broken up by forces acting beneath, and by currents above, are not to lie lost sight of in our 

 geological researches. 



Origin of the Magnetic and Specular Oxides of Iron. 



I have had occasion so frequently to refer to igneous action, in my remarks upon unstrati- 

 fied and subordinate rocks, that I have already anticipated the views which I am about to 

 present of these two oxides. It will be seen from the structure of the diagram, and from the 

 general bearing of the facts, that such an origin is by far the most probable, though there arc 

 many geologists who maintain the theory of electro-magnetic agency ; and it must be con- 

 ceded that it possesses many plausible points, and a few facts which lend it some support. 

 Still as it regards its establishment, it appears from the researches of Farada3% that we should 

 be obliged to sustain it on the assumption that the materials must have been in a liquid state 

 at the time of their formation ; as the principle of electro-magnetism has no power to act 

 upon a substance, so as to transfer it from one point to another, if it is in a solid or aeriform 

 state. Electro-magnetism, though it decomposes water, is unable to act upon ice, or to de- 

 compose any other substance when solid ; this at least is the case in the experimental researches 

 of the most eminent philosophers of the day, in relation to tlie decomposing and transferring 

 power of this agent. 



The igneous origin of both oxides rests partly, as already stated, upon the establishment of 

 the plutonic character of the rocks associated with tliem, and partly upon the mode of their 

 occurrence in those masses. It is true, that the specular oxide appears among the lower 

 layers of a sedimentary rock ; but a careful inspection will satisfy most observers that it 

 appears here as an intrusive rock, and that it has been forced into this position subsequent to 

 the deposition of this sandstone ; the evidence of which appears in the facts which have 

 been stated in the preceding pages, viz. its fractured and upraised position. And it is not at 

 all remarkable that a porous sandstone should have been penetrated by this material, so as to 

 appear somewhat homogeneous, when we consider the forces which must have acted previous 

 to, and during its upheaval. 



I have noticed, also, and it is a fact which has the same bearing as the others already stated, 

 that some portions of the rock adjacent to the ore are porous, or somewhat vesicular : the 

 pores are, however, quite small, but still they are quite characteristic, and are clearly different 

 from that kind of porosity which arises from decomposition ; they appear, in a word, like 

 those in the sandstone of Connecticut river, in the vicinity of the greenstone trap. Of the 

 origin, then, of the oxides of iron, there are a variety of facts of the same character, which, 

 when observed in other rocks, have been considered demonstrative of an igneous origin : if, 

 then, we are not in error in relation to principles already received, we can scarcely refuse to 

 apply them to the question of the origin of the ores of iron. 



In concluding my observations on the origin of the ores of iron, I feel more desu'ous of 

 Geol. 2d Dist. 13 



