APPENDIX. 



637 



MODE XV. Arseniate of 

 Iron. 



STRUCTURE I. Crystallised. 

 II. With Copper. 



MODE XVI. Green Iron 

 Earth. 



Aspect 1. Friable. 

 2. Coherent. 



This may be compared with 

 the Petralogy, in regard to the 

 Structures and Aspects. The 

 genera of Thomson have not 

 been admitted by other writers, 

 who arrange all* the species in 

 s accession, without dividing them 

 into genera. But as these large 

 divisions of Thomson seem very 

 useful, they might be retained 

 under the name of Nomes, or 

 subsidiary districts. 



In Lithology Dr. Thomson not 

 having admitted Orders or Ge- 

 nera, but only Families and Spe- 

 cies, no confusion could arise; 

 and the Modes belong to the 

 mixtures of the same substance, 

 as Strpntian is one Mode, and 

 Celestine is another ; that is, the 

 Species of Werner become 

 Modes, while his Subspecies be- 

 come Structures. 



In like manner if we take Iron 

 the first Species, Native Iron is a 

 Mode, or special chemical com- 

 bination. The second Species, 

 Iron Pyrites, is another Mode 

 with four Structures, Compact, 

 Radiated, Cellular, and Capil- 

 lary ; the Hepatic being an As- 

 pect. The fourth Species, Mag- 

 netic Iron-stone, is also a chemi- 

 cal Mode of great importance ; 

 whereas in following Dr. Thom- 

 son's arrangement it is merely a 

 Structure, while there is not only 



nothing particular in its exterior 

 Structure, but its Aspects, the 

 Compact, Laminar, and Crystal- 

 lised, are real Structures. The 

 fifth Species is SpecuJar Iron 

 Ore, which becoming a Structure 

 instead of a Mode, the terms 

 Massive and Crystallised, winch 

 belong to Structure, become 

 mere Diversities. In the others, 

 Amorphous, Crystallised, Com- 

 pact,Columnar, Pisiform, Earthy, 

 become Aspects instead of Struc- 

 tures. 



It is therefore necessary in the 

 Metals, as in the Earths, that 

 each new Species or different 

 combination, for example, with 

 Carbon, Arsenic, &c. or with dif- 

 ferent modifications of various 

 Earths, should be called a Mode, 

 as in the other provinces that 

 word supplies the term Species, 

 and implies in itself a new mode 

 of chemical combination ; and in 

 this way only can the term Struc- 

 ture revert to its original destina- 

 tion. 



The classical word Nome, de- 

 rived from Egypt, the pa' nt 

 country of Chemistry, may be 

 found very appropriate, as al- 

 ready explained. 



The dignity and importance of 

 the Metals also require a multi- 

 plication, instead of a diminution, 

 of the higher terms in the nomen- 

 clature. Nor must it be forgot- 

 ten that the very nature of the 

 subject, in which the substances 

 and their qualities are of them- 

 selves various and vague, would 

 render any attempt at mathema- 

 tical precision rather pedantic 

 than useful or distinct (me quali- 

 ties, like the substances them- 

 selves, often passing into each 

 other); and that every system, 

 even the Newtonian, has its ano- 

 malies. 



