106 0. H. Smyth, Jr. — Alnoite containing Melilite. 



the rule is of particular interest. Artificial melilite of posi- 

 tive character has been described by Vogt* and by Bodlander ;f 

 but even so recent a work as the third edition of Rosenbusch's 

 " Mikroskopische Physiographie der petrographisch wichtigen 

 Mineralien," though implying the probable existence of a posi- 

 tive molecule in ordinary melilite, does not definitely state 

 that the mineral is sometimes positive in rocks. As a rock 

 constituent melilite of a positive character has been mentioned, 

 so far as the writer knows, only by Becke.J He refers to two 

 nepheline basalts containing melilite of positive character ; 

 and as an explanation states that " man wird nicht fehlgehen, 

 wenn mann annimmt, das die gesteinbildenden Melilithe 

 isomorphe Mischungen von zwei Endgliedern seien, von 

 den en das eine mit negativer ]?oppelbrechung wohl im vesu- 

 vischen Humboldtilith vorliegt, wahrend das positive noch 

 unbekannt ist." This explanation is in accord with the facts 

 observed in the Manheim rocks, as well as with the observa- 

 tions of Yogt, who was led to a similar conclusion in regard to 

 the artificial melilite. Bodlander, however, holds that this 

 view is inconsistent with the results of analyses of artificial 

 melilite, and concludes that the mineral is positive when it 

 contains a large amount of magnesium.§ 



With the view of obtaining further evidence as to the occur- 

 rence of positive melilite, sections of. five other rocks contain- 

 ing the mineral have been carefully examined. The rocks are 

 melilite basalts from Wartenberg, Bohemia, and Hochbohl, 

 Wiirttemberg; leucitite from Capo di Bove, Italy; and 

 alnoites from Alno, Sweden, and Ste. Anne, Canada. All of 

 these localities with the exception of the last, are so noted as 

 to be almost classic. The sections of the first three rocks 

 were prepared by Yoigt and Hochgesang in Gottingen. For 

 the sections of the two alnoites, as well ts for other assistance, 

 the writer is indebted to Professor George JEL Williams. 



While in all of these rocks the ordinary negative melilite 

 predominates, in two of them, the melilite basalt from Warten- 

 berg and the alnoite from Alno, the positive variety exists to 

 some extent. In both rocks it forms entire laths like those in 

 the Manheim rock, being particularly abundant in the basalt. 



Although, of course, it does not follow that in an examina- 

 tion of a larger number of rocks as great a proportion would 



*Yogt, J. H. L. : Studier over Slagger, Stockholm, 1884; also Beitrage zur 

 Kenntniss der Gesetze der Mineralbildung in Schmelzniassen und in den neovul- 

 kanischen Ergussgesteine, ChristiaDia, 1891. 



f Bodlander, G. : Entstehung von Melilith beim Brennen von Portland-cement, 

 Neues Jahrbuch fur Mineralogie, etc., 1892, I, p. 53. 



JBecke, F.: Optischer Charakter des Melilith als Gesteinsgemengtheil, Tscher- 

 mak's Mittheilungen. xii, p. 4.44. 



§Op. cit.. p. 56. 



