FOYAITE-IJOLITE SERIES OF MAGNET COVE 



651 



Within the limits from II to VI the curves are simple, that 

 of SiOg alone showing inflexion about at the center of the dia- 

 gram, rising sharply toward the right (acid end) and falling 

 gently toward the left (basic end). Most of the curves are quite 

 flat, especially those of AI3O3, Na^O and K3O, which approx- 

 imate straight lines. At the same time they are all distinctly 



SiO, 



VIII 



Diagram 



curves and not strictly linear. ' It will be remembered that 

 Pirsson^ says that all of the lines of his diagram should prob- 

 ably be drawn as very flat curves (much flatter than these), and 

 these observations are in accordance with the conclusion of 

 Harker,3 that strictly linear series of rocks are of rare occur- 

 rence. 



With the exception of SiOg, which is inflexed and that of 



' This is best seen in tlie large-scale drawing from which the diagram is repro- 

 duced. 



*L. V. PiRssoN, op. cit., p. 571. 



3 A. Marker, Jour. Geol., Vol. VIII, p. 392, 1900. 



