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NEW YORK STATE MUSEUM 



augite syenite and gabbro, are very suggestive. Like the inter- 

 mediate rock of column 0, it departs most widely from both the 

 syenites and the anorthosites in its magnesia percentage, the 

 general Adirondack intrusives being abnormally low in that oxid. 

 It occupies an intermediate position between syenite and gabbro, 

 rather than between syenite and anorthosite, and as such is nearer 

 syenite than gabbro chemically. Through the kindness of Profes- 

 sor Smyth, the writer is in possession of a slide and specimen of 

 this rock. The analysis gives the iron as all in the ferrous con- 

 dition, but there is quite a little magnetite in the rock, and a 

 rough calculation indicates its approximate composition to be 

 21$ orthoclase, 30.75$ albite, 13.75$ anorthite, 3$ magnetite and 

 25$ augite and hornblende. The feldspar content is quite like 

 that of the preceding rock, the augen consisting of labradorite 

 and the granular feldspar of microperthite and acid plagioclase. 



The remaining seven analyses, no. 10 excepted, are all of un- 

 mistakable syenite and gave an excellent representation of its 

 variation. The ferrous iron percentage is mostly high, and the 

 results of some of the analyses tend to throw doubt on the relia- 

 bility of the entire series of ferrous iron determinations, and 

 hence to greatly complicate attempts to calculate the mineral 

 percentages. The two most clearly abnormal results are those 

 of analyses 9 and 13. In the former case the result of the fer- 

 rous iron determination exactly equaled the total iron in the 

 rock, yet the thin section showed considerable magnetite 

 present, and a rough separation by means of heavy solutions 

 and a bar magnet proved the presence of at least 5$ of that 

 mineral. In the latter case the total iron present is 3.42$, yet 

 the ferrous iron result exceeded 5$. While only these two were 

 on their face erroneous, others, such as nos. 10 and 11. are quite 

 suspicious. The disturbing cause can not be pyrite, since there 

 is so little of it present that the sulfur percentage does not in 

 general reach .01$. It is difficult to see how carbonaceous 

 matter other than graphite can be present, and in an igneous 

 rock any considerable amount of graphite would be surprising. 

 The cause of the vitiation is as yet undetected. 



The only analysis so far made of the augite syenite which 

 occurs cutting the anorthosite, analysis 8, indicates that to be 



