92 



THOMAS STEEEY HUNT ON A NATUEAL SYSTEM IN 



divided the order of Silicates. In these tables the principal atomic ratios are given in 

 the left-hand columns, while more rarely recurring ratios, as in danalite, schorlomite, 

 sloanite, etc., are placed in parentheses after the names of the species, which are in their 

 appropriate positions in their respective columns. In the case of Trilje 4, the exigencies 



Suborder III. Persilicate. 



of construction have caused its displacement in the table, and hence the atomic ratios 

 of its included species are there also appended. The calculated values of V are given 

 with the respective tribes. These tables are necessarily much abridged, and should be 

 studied in connection with the systematic grouping of suborders, tribes and species to be 

 found under § 55 of the present essay. 



Contents of Sections. 



I. — Historical Introduction. — § 1. Classification in natural history. — 2. Werner's system in mineralogy. — 3. The 

 work of Mohs and Jameson ; the natural-history method. — 4. The orders and genera of Mohs. — 5, 6. 

 His system adopted by Shepard and J. D. Dana ; the question of nomenclature. — 7. The chemical 

 system of Berzelius ; adopted by Rammelsberg, Dana and others ; its defects.— 8, 0. Aims and objects 

 of a natural system in mineralogy. 



II. — An Attempt at a Natural Sijsiem. — § 10. The system proposed and defended by the writer, 1853 — -1855. — 11, 

 12. Restated in 1867 ; high molecular weights, complex formulas, substitution, homologies, suscep- 

 tibility to chemical change and hardness as related to atomic volume. — 13, 14. Scope of mineralogy ; 

 principles of classification. — 15. The carbon series and the silicon series ; relations of molecular weight 

 to specific gravity'in solids. — 16. Progressive or homologous series in mineral compounds maintained. 

 — 17-19. Polysilicates and polycarbonates; molecular volumes. — 20, 21. Chemical notation; atomic 

 formulas.— 22. Hypothesis of crystalline admixtures; Delesse, Scheerer, Von Waltershausen. — 23. 

 Defined by the author.— 24. Adopted by Tschermak. — 25. The hypothesis criticised. — 26. Bases of a 

 natural system as defined in 1S54.— 27. Aug. Laurent on natural silicates ; divisibility of molecules. — 

 28. Ad. Wurtz on polysilicates. — 29, 30. Saussurite and its relations to meionite ; reduction of densi- 

 ties by fusion. — 31. The scapolites and jadeite. — 32, 33. Volumes deduced from atomic formulas. — 

 34. Weight of atomic units. — 35. Synopsis of principles. 



