184 H. p. ri'SHTXG — ArGITE-SYKNITE GKKTSS XEAE LOOX LAKE 



lestly iin])0ssibl<» here. The only way of iiit(^rpreting- the analysis that 

 suggests itself to the writer is to assume that the augite is essentially a 

 lime, ferrous-iron, alumina silicate, unusuall}^ high in the last named 

 oxide. 



Cnhahdlon <{( A iKiit/xix 1 



lai 



8iO, 10575 



TiO; 9 



ALOj , 1795 



FeA 25 



Feb I 494 



HtiO 8 



Oi(; 52;] 



:SU^O 87 



K.,0 ^ 547 



Ka,0 i SU 



Molec'u- Magno- Ortlio- ,„„•.„ AiKir- 1 Hj'per- 1 ,„„,•.„ ' />nnrf-/ 

 :arrati<..l tiTe. clanp. '^''"^'^- thite. ' sthene. ' *-^"8''^''- i *^"'^"'^- 



9 



:]-js2 



4890 



;]18 



17i 



745 ' 



1 



IKJO 



26 



35 







547 



81(> 



159 





0/2 1 











87 



:]72 1 











.8 

 151 









87 



r'j72 ' 







547 



'"816 













1 









0.7;] 



30.;]9 



42.70 



4.51 



2.02 



12.02 1 



1 



7.07 



This result agrees quite well with that ohtained by separation with 

 heavy solutions, and can not be far from the actual composition of the 

 rock. As it stands, the plagioclase is albite, Abjj, An^, and the micro- 

 perthite is ai)proximately Or.^ Ab.. The plagioclase is in all probability 

 not quite so acid as this would imply, as the augite undoubtedly contains 

 a little soda, wdiich would disph\ce some of the lime calculated in that 

 mineral, and both lower the albite and raise the anorthite i)ercentage. 

 It is thought that this change is onh'' slight, not materially affecting the 

 calculation. 



The agreement between analyses I and II is exceedingly close. The 

 Diana rock is even more feldspathic than that from Loon lake, which 

 accounts for the increased silica and diminished lime and magnesia of 

 the former; but the rock at Loon lake is quite variable, and specimens 

 could be selected which would tally almost exactly with the Diana 

 analysis. No doubt also the converse is true. 



Of the other available published analyses of American syenites, the 

 two which stand nearest the Adirondack rock are quoted in columns III 

 and IV of the table. Of the Mount Ascutney syenite, no published petro- 

 graphic description is available.* A hand specimen and slide in the 

 writer's possession show a green feldspathic rock very similar to that 



* J)r Daly partieipiited in the discussion following the reading of the paper before the Society, 

 stating that the relations of the roeks of mount Ascutney had been carefully worked out and were 

 in preparation for publication, and emphasizing the similarity of the Loon Lake rock. 



