CHEMICAL ANALYSES AND DISCUSSION 



489 



adjacent rock along this portion _ of the border is anorthosite gabbro. 

 If there has been incorporation of material from the anorthosite by 

 this syenite, it is but fair to assume that the assimilated rock was not 

 mere gabbro, but anorthosite gabbro. No analysis of the typical anor- 

 thosite gabbro of the region is available, the rock from Eand hill, Clinton 

 county, a distant locality where the rock occurs as an outlier instead of 

 as a portion of the great anorthosite bathylith, being the only one so far 

 analyzed. Like the rock of most of the outliers, this is of a somewhat 

 abnormal type, being certainly higher in alumina and lime and lower in 

 iron and magnesia than the usual anorthosite gabbro. Study of the 

 slides of the Tupper Lake rock, however, suggests that its composition 

 would be quite similar to a half and half combination of this Eand Hill 

 rock, whose analysis appears as number 3 of the table, with that of the 

 gabbro of number 2, and the calculation is then made of a combination 

 of this with the normal syenite of number 11 in the proper proportions 

 to obtain a rock of the silica percentage of the medium basic syenite of 

 number 9. In the following table columns 1 and 2 are the respective 

 analyses of the gabbro and anorthosite gabbro, column 3 a combination of 

 50 per cent of each, column 4 the syenite, column 5 the result of com- 

 bining 3 and 4 on the basis of 26.8 per cent of the former and 73.2 per 

 cent of the latter, while column 6 gives the analysis of the basic syenite 

 for comparison with the calculated composition of the mixture, and 

 column 7 the discrepancies between the two. 



SiO,. . 

 Al,03 

 Fe^O,, 

 MgO. 

 CaO.. 

 Na^O 



1 



2 



3 



4 



5 



6 



47.42 



51.62 



49.52 



63.45 



59.7 



59.7 



17.34 



24.45 



20.89 



18.38 



19.05 



19.52 



15.13 



6.95 



11.04 



3.98 



5.87 



6.81 



5.21 



1.21 



3.21 



.35 



1.11 



.78 



8.09 



9.97 



9.03 



3.06 



4.66 



3.36 



3.48 



3.49 



3.48 



5.06 



4.63 



5.31 



1.89 



1.27 



1.58 



5.15 



4.19 



4.14 



98.56 



98.96 



98.75 



99.43 



99.21 



99.62 



— .47 



— .96 

 4- .33 

 +1.3 



— .68 

 + .05 



Here is a large discrepancy in lime and considerable ones in other 

 constituents. These are thought to be due in part at least to unsound- 

 ness in the original assumption that the rock of column 3 is closely akin 

 to the anorthosite gabbro of the district, the trouble arising from the 

 abnormal character of the rock of column 2. But inspection of analyses 

 8-10 of the original table, all of which are basic syenites of not widely 

 differing silica percentages, shows much variation in all the constituents 

 which show the main discrepancies here, so that if either number 8 or 



