REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 r73 



feldspars, the rock distinctlv approaches the syenitets, though its 

 silica percentage remains that of the normal anorthosite. 



The gabbro of column 7 is a most interesting rock. Its occur- 

 rence with, and as a differentiation product of an augite syenite 

 iDody, of which it must be regarded as a basic phaise rather than 

 as a true gabbro, and its intermediate position chemically 

 between augite syenite and gabbro, are very sugge(Stive. Like 

 the intermediate rock of column 6, it departs most w^idely from 

 both the ^syenites and the anorthosites in its magnesia percentage, 

 the general Adirondack intruisives 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 Prof. Smyth, the writer is in possession of a slide and specimen 

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

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

 a rough calculation indicates its approximate composition to be 

 21^ ortho'clase, 36.75^' albite, IS.lofo anorthite, Zfc magnetite and 

 25^ augite and hornblende. The feld*spar 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 unmis- 

 takable syenite and gave an excellent representation of its varia- 

 tion. The ferrous iron percentage is mostly high, and the results 

 of some of the analj^es tend to throw doubt on the reliability 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 ferrous iron deter- 

 mination 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 ca"se 

 the totad 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 disturb- 



