394 PKOF. P. MARSHALL OlS" THE SEQUENCE OF [Dec. 1914, 



Chemical Composition of the Lavas of 



H 



ST 



SiOo '65-34 59-54 49-10 



pq 



Ti0 2 0-12 0-38 



! 



AI0O3 18-56 19-04 



Fe 2 3 



FeO 



MgO 



CaO 



K 2 



Na 2 



P 2 5 



Totals.., 



1-28 

 0-92 



4-72 

 2-48 

 ... I 0-31 

 1-20 2'68 

 4-17 



o 00 

 6-79 

 0-21 

 100 



6-25 

 0-43 



2-16 

 14-30 

 5-78 

 9-52 

 435 

 935 

 1-73 

 3'41 

 030 



-* 



100 100 



48-10 

 2-36 



16-03 

 7-96 



10-10 

 2-36 

 7-33 

 114 

 4-35 

 0-27 

 100 



03 <x 



PP PS 



49-10 45-05 48-31 49-06 



2 03 2-53 

 16-08 13-01 



5-14 

 9-64 

 3-04 

 919 



7-64 



8-37 



2-43 



15-17 

 6-39 

 8-63 



8-20 J 2-87 

 10-71 i 9-82 



1-64. 1*77 2-60 



3-85 i 2-34 

 0-29 : 0-38 



3-18 

 0-60 



100 1 100 ; 100 



2-57 



15-24 



5-34 



9-70 



2-52 



10-20 



1-54 



46-91 46-74 46*84 



3-58 

 15-25 

 6-42 

 8-36 

 4-45 

 10-40 

 1-25 



3-42 I 3-13 



0-41 I 0-25 



344! 233 



100 1 100 



13-28 



7-68 

 10-77 

 3*55 

 9-57 

 1-10 

 3-55 

 0-32 



17*04 



48-67 



244 



16-09 



6-21 1 3*92 

 9-64 j 9-76 

 3-25 I 4-67 



10-35 

 0-46 

 367 

 0-21 



9-30 

 1-06 

 3-58 

 0-51 



100 100 I 100 



These analyses have been recalculated to 100 after subtraction of the 

 disturbing factor when comparing these analyses. The loss 



1-20 4-68 4-00! 6'02 5*21 4'00 4"20 5*38 



5-32 6*72 5-42 6*61 



abundant nepheline in such a rock. The two succeeding basalts 

 exhibit no marked characteristics, and No. 24 is, again, a rock 

 that chemically, at least, is a connecting-link and may perhaps be 

 best called a trachydolerite, as it is much higher in alumina and 

 lower in silica than the kaiwekite (No. 13). The final phonolite 

 is comparable with No. 2, and like it is distinctly less alkaline 

 than No. 14, which contains a large quantity of nepheline and 

 senigmatite. 



In order to facilitate a comparison between the different rocks, 

 two curves have been prepared (Pis. LIII & LIV). In both of 

 these the abscissae merely indicate the position of the rock in the 

 scries of lavas. In PL LIII the ordinates represent the molecular 

 proportions in which the various constituents are present in the 

 rocks. The diagram brings into prominence these two facts : — 



(1) The fourfold alkaline development in the series, and (2) the conspicuous 

 extent to which Nos. 13 and 24 are intermediate between the phonolites and 

 basalts in composition. 



