J". D. Whitney on the Ores of Iron in the Azoic System. 43 



bedded, and the ore shows a greater tendency to cleave into thin 

 laminae parallel with the bedding, in proportion to its freedom 

 from silicious matter. These deposits seem to have been of sedi- 

 mentary origin, having been originally strata of silicious sand, 

 which has since been metamorphosed. The iron ore may have 

 been introduced either by the sublimation of metalliferous vapors 

 from below during the deposition of the silicious particles, or by 

 precipitation from a ferriferous solution, in which the stratified 

 rocks were in process of formation. 



The great deposits of ore which have been alluded to above, 

 agreeing as they do in the characteristic features of their mode 

 of occurrence, especially in the magnitude of the scale on which 

 they are developed, are all, beyond doubt, situated in the same 

 geological position ; they all belong to the oldest known system 

 of rocks, the azoic. This name was first applied by Murchison 

 to the ferriferous rocks of Scandinavia, and the geological posi- 

 tion of the great iron regions of this country is precisely similar 

 to those of Sweden. There is ample evidence that the lowest 

 known fossiliferous strata, characterized by the same peculiar 

 types of organic life, both in this country and in Europe, rest 

 uniformly upon the iron-bearing strata throughout the Northwest, 

 from New York to Missouri and Arkansas. 



We have thus seen that the earliest geological epoch was char- 

 acterized by the presence of the ores of iron in quantity far 

 exceeding that of any succeeding one ; indeed, we may infer that 

 the ruins of the iron ores of this class have furnished the mate- 

 rial from which many of the ores of more recent geological age 

 may have been derived. The condition of things in reference to 

 the ores of iron which existed during the azoic period underwent 

 a complete change, and rarely do we find in any fossiliferous rocks 

 any signs of unmistakably eruptive ores. It is certain that we 

 nowhere, out of the azoic system, find masses of ore of such extent 

 and purity as those which have just been alluded to. By far the 

 larger portion of the azoic series on the earth's surface being cov- 

 ered up by the fossiliferous rocks, the ore which that formation 

 contains is equally concealed, and it is only in those regions 

 where no deposition of newer strata upon the oldest rocks has 

 taken place that the treasures of iron are made accessible. In this 

 respect our country is preeminently favored, and there can be 

 no doubt that the immense deposits of iron ore stored away in 

 the Northwest are destined at some future time to add to our 

 national wealth more than has been or ever will be contributed 

 by the gold of California. It may seem absurd to speculate on 

 the exhaustion of the stratified ores of England or of the Eastern 

 United States ; yet nothing is more certain, than that the present 

 rate of production in the former country cannot be kept up for 

 any very great length of time, without making the cost of pro- 



