l)r Colqiihoun on the Argillaceous Ore of' Iron. 212 



Our design to give, as far as possible, a complete view of the 

 various progressive stages by which a knowledge of its true 

 constitution was acquired, as well as of the manner in which 

 it is made to perform so important a part in the manufactures 

 of the country, we shall begin by taking a rapid glance at the 

 different opinions which have been entertained respecting it 

 by successive mineralogists down to the present day. 



When we consider the ardour with which metallurgic che- 

 mistry had already been cultivated, at the commencement of 

 the present century, by many distinguished chemists and mi- 

 neralogists, and reflect on the comparative accuracy with 

 which they had determined the composition of many of the 

 more rare and curious among the native compounds of iron, 

 it cannot fail to excite surprise that other ores of that metal, 

 and those the earliest known, the most widely distributed, and 

 the most valuable in commerce, had been examined by them 

 so superficially. The composition of the hydrates of the per- 

 oxide of iron remained unknown till their nature was deter- 

 mined in J 810 by the researches of D'Aubuisson ; and the 

 argillaceous carbonate of iron was for even a longer period ne- 

 glected. It was generally considered a mere mixture of clay 

 and the peroxide of iron, and was classed in min^ralogical 

 systems along with the hydrates of the peroxide of iron, or, 

 as they were commonly termed, the iron ochres and hematites. 

 This erroneous arrangement was countenanced by some su- 

 perficial chemical analyses, but it was principally founded on 

 a loose examination of the general external appearance of the 

 ore, together with the analogies suggested by its geological 

 position and by the nature of the minerals with which it was 

 found associated. 



Werner was the mineralogist who made the first important, 

 though still very imperfect step, towards the extrication of 

 this mineral from a mass of others of an essentially distinct 

 nature, with which it had previously been confounded. His 

 acute discrimination could not fail to detect the marked dif- 

 ferences in external character, which separate the argillaceous 

 carbonate from the native peroxide, and hydrated peroxide of 

 iron ; and accordingly, after describing these two latter ores 

 under the appellations of Brauneisenstein and Rotheisenstein, 



