38 CLASSIFICATION BASED OX MINERAL COMPOSITION. 



Amongst those who have acknowledged Hunt's claim are both Daiias,* 

 Silliman,t Leeds, t RLitley,§ Hawes, || and Fouque and Levy. ^ 



Edward Dana says that the theory " was offered by Hunt, and has since 

 been developed by Tschermak ; " Rutley, that Hunt's conclusions are almost 

 identical with those of Tschermak ; again, James D. Dana, mistaking Hunt's 

 views, stated of the latter, " In the view . . . with regard to the molec- 

 ular relations of the feldspars, he appears to have anticipated Tschermak by 

 ten years;" while Silliman goes so far as to say, " Here will be found devel- 

 oped his [Hunt's] views on the constitution of the feldsjjars, which were 

 some years later adopted without acknowledgment by Tschermak." Leeds 

 appears to have been the only one who recognized the essential difference 

 between the indefinite mechanical-mixture view adopted by Hunt, and the 

 definite molecular-union theory of Tschermak ; but he failed to see the logical 

 conclusion to be derived, — that Hunt** was in no sense the originator of 

 Tschermak's theory, and that all the charges of appropriation made against 

 the latter ought to be entirely withdrawn. 



In 1875, Descloizeaux, from the optical properties of the plagioclastic feld- 

 spars, concluded that andesite was an altered oligoclase, but that labradorite 

 and oligoclase are distinct species, and not isomorphous mixtures. He looked 

 upon their optical properties as opposed to Tschennak's theory. ft To explain 

 the chemical composition, Descloizeaux calls attention to tlie theory of 

 Friedel and others, that the several feldspars differ from one another only 

 in their proportions of silica, forming a series whose common difference is 

 Si02 : c- (J., anorthite -(- SiOo = labradorite ; labradorite -|- SiOg = andesite ; 

 andesite -|- SiOa = oligoclase ; and oligoclase -|- SiOa = albite. 



While Descloizeaux admits that the composition of the feldspars may be 

 explained as well by Tschermak's theory as by Fi-iedel's, yet he holds that 

 the latter accords better with the optical and crystallographic characters of 

 the species. 



Vom Rath, on the other hand, is of the opinion that the chemical consti- 

 tution of tlie feldspars is most satisfactorily represented by Tschermak's 

 theory, and holds that the formation of the intermediate triclinic feldspars 



* Am. Jour. Sci., 1S75 (3), ix. 102 ; Test Book of Mineralogy, 1S77, p- 297. 

 f Amer. Chemist, lS7-t, v. 106. % Aiiier. Chemist, 1S77, vii. 335. 



§ The Study of Rooks, 1S79, p. 95. 1| Geol. New Hampshire, 1878, iii. part 4, p. 89. 



•^ Miner. Microg., 1879, p. 200. 



** Bull. Mus. Comp. Zool., 1S84, vii. 370-374, 445-454, 458, 450. 



ft Ami. Chimie Ph.vsiq\ie, 1875 (5), iv. 429-444; Comptes Reudus, 1875, Ixxx. 364-371; Neues Jahr. 

 Miu., 1875, pp. 279-284, 395-399. 



