Smyth^ Jr. — Petrography of Dikes in Syracuse, N. Y. 29 



The mineral is probably pyroxene, but the limited quantity 

 hardly admits of accurate determination. 



Aside from the variations described, this rock differs in no 

 marked degree from the first dike rock described, except that 

 one section shows tiny prismatic crystals of pyroxene in the 

 groundmass. On account of its excessive alteration, sections 

 of the rock are largely made up of secondary products, but 

 these are essentially the same as those described above. 



Of the two classes of inclusions, Paleozoic and pre-Cambrian, 

 the former are naturally more abundant. The fragments are 

 often angular and sometimes show a faint zonal coloration 

 along the contacts. But there is no decided indication of new 

 mineral growth. The pre-Cambrian fragments are usually 

 more rounded, the result of the attrition involved in their 

 upward journey of many hundred feet. They do not differ 

 materially from inclusions described in other dikes of the 

 region. 



In comparing the rocks of this locality with specimens from 

 DeWitt and from Green st., as might be expected, a strong 

 family resemblance is apparent. There is perhaps less mica 

 and rather more perofskite in the Butternut st. rocks, while 

 only one section shows the tiny crystals of pyroxene that are 

 so abundant in the groundmass of the DetVitt dike. But 

 these differences are much too slight to be of any moment. 



Melilite in the Green St. Dilie. — The marked resemblance, 

 both in petrography and geological relations, between the 

 Syracuse rocks and the alnoite of Manheim has led the writer 

 to expect, at any time, the discovery of melilite in the former. 

 In studying the DeWitt rock, Prof. Kemp- searched carefully 

 for this mineral but found none. The writer's study of the 

 Butternut st. rock met with the same result; but in the exami- 

 nation of the rock of the original Green st. dike of Williams,t 

 melilite was found. This seems at first sight surprising, as, 

 doubtless, sections of the rock have been examined by many 

 petrographers ; but the fact that melilite has not been noted 

 before simply illustrates the elusive nature of the mineral, 

 resulting from its tendency to alteration. In the case of the 

 original Manheim dike, the rock was first described by the 

 writer:]; as a peridotite and its true nature was learned only 

 when fresher material was procured ;§ while in the largest 

 dike of that locality no melilite could be determined with cer- 

 tainty, although there can hardly be a doubt of its original 

 presence.! 



Some years ago a section was made from a specimen of the 

 Green stc dike which very closely resembled the original 



* Loc. cit. t This Journal (3), xxxiv, pp. 137-145. 



tibid. (3), xliii, pp. 322-327. gibid., xlvi, pp. 104-107. 



II Bull. Geol. Soc. Am., ix, pp. 257-268. 



