3^0 Dr Colquhoun on the Argillaceous Ore of' hwi. 



he constitutes the former a distinct species, under the names of 

 Gemeiner Thonargiter-eisenstein, Thoneisenstein, Eisenthon, 

 &c. But Werner laboured under the popular error of consi- 

 dering that the argillaceous carbonate consisted of a mixture 

 of clay with the oxide of iron, and he was therefore led in 

 many cases to confound it with other ores differing essentially 

 in their chemical constitution, but possessing a strong analogy 

 in their physical properties. Thus, in describing the several 

 varieties of his Thoneisenstein, he assigns to them mineralogi- 

 cal characters, and even geological situations, which can only 

 be referred to minerals containing the peroxide of iron. 



Werner's high reputation caused his classification to be im- 

 plicitly adopted by almost all the mineralogists of Germany, 

 for a period of twenty years, and established it also in the 

 systems of many distinguished men in other countries. The 

 ore is accordingly to be found arranged, with little variation 

 from his method, in the systems of Breithaupt, Hoffman, 

 Brochant, Kirwan, Brogniart, Jameson, and others. 



Among these followers of Werner, there was one, however, 

 Kirwan, who, in his Elements of Mineralogy^ published in 

 1794, had the merit of advancing somewhat towards ascer- 

 taining the distinct character of the argillaceous carbonate of 

 iron. It is true that he still classed it under the " calces of 

 iron, mixed with a notable proportion of clay," and termed it 

 common argillaceous ironstone. But, although ignorant of 

 the real composition of the ore, he nevertheless gave an accu- 

 rate account of its mineralogical characters, and separated it 

 from the numerous varieties of oxide and hydrated oxide of 

 iron, with which it had previously been confounded.* 



Jameson, in the third edition of his System of Mineralogy^ 



* Vol. ii. p. 173. Mr Kirwan's description was drawn up principally 

 from the minerals which were at that time smelted in the Iron Founderies 

 of Carron. '' Of which," says he, " as Mr Jars (in his Voyages M^tallur- 

 giques) gives no particular account, though he says that in all his travels 

 he met none like it, I hope a detailed description will not be unaccepta- 

 ble." That he had not the slightest suspicion, however, of the true che- 

 mical constitution of this ore is clearly evinced in a subsequent para- 

 graph, where he classes along with it the '' trappose ore used in Sweden, 

 of which the whole mountain of Taberg is said to consist, and which, by 

 Chevalier Napion's account, is a trap overloaded with iron." 



