Dr Colquhoun on the Argillaceous Ore of Iron. 2^3 



overrated the quantity of alumina at the expense' of the oxide 

 of iron, but it is also established, that the ores consisted es- 

 sentially of carbonate of protoxide of iron, and that the car- 

 bonate was argillaceous. As the results of the analyses only 

 occupied a subsidiary place in the chemist's attention, he has 

 not given any description of the mineralogical characters of 

 these specimens, or of the minerals with which they had been 

 found associated in their natural deposits. 



After the period when Richter published his essay, the na- 

 ture of the argillaceous carbonate of iron seems to have met 

 with little regard until the year 1812, when it was excellent- 

 ly illustrated, both as to its chemical and mineralogical charac- 

 ters, by M. Collet- Descostils. * This acute chemist, who 

 held the situation of director of the Ecole des Mines, had fre- 

 quent occasion to examine specimens of the ore collected from 

 different quarters of France, and also from England. In his 

 Notice sur une des Especes de Mineral de Fer, reunies par 

 plusieurs Miner alogistes sous le nom de Fer Argileux, -f- he 

 fully developes the true chemical constitution of the ore, he 

 accurately describes its external and physical characters, and 

 he gives a correct account of the geological positions which it 

 usually occupies, and to which it seems to be confined. 



The result of Descostils's researches was very important to 

 mineralogy, in clearly establishing the distinct and peculiar 

 nature of the chemical composition of the argillaceous carbo- 

 nate of iron ; but it was still more so in a geological point of 

 view. For he discovered, to his surprise, that the country of 

 France, in many of its districts, abounded as much in this most 

 valuable ore of iron as the island of Great Britain itself. Upon 

 examining a variety of specimens which were collected from 

 different localities in France, and one that had been procured 

 from Colebrook Dale in England, Descostils found, that, not- 

 withstanding their dull earthy aspect, they all possessed exact- 



• It is true that before that period both Drappier, (1805, Journal dei 

 Mines, xviii. 50. Note,) and Berthier, (1809, Annales des Mines, iv. 359,) 

 had made a correct analysis of certain specimens of the ore. But Descos- 

 tils was the fii-st who gave to the public a complete account of its nature, 

 composition, and geological history. 



t Annales de CheTnie,\xxxi\. 188. 



