956 THE JOURNAL OF GEOLOGY. 
TABLE VI. CHEMICAL ANALYSES OF GRORUDITE, SOLVSBERGITE, 
TINGUAITE. 
I 2 3 4 5 6 ii 8 
SiO, Fines | Yemen yilesiy OHO OCH Orzo) Soo SEK 
WiOa (Ge Zits) e Ac 65 .50 35 tr. .Q2 .40 soe 
Al,O3 S37) 10.60) 12:21) S14. co 1G 30 lO On 7h OmmOLo 
Fe,0, 5-84 BF 4.53 BND 3.62 3.34 3.94 3.18 
FeO 1.00 7c 1.14 3.56 84 2.35 D7] 56 
MnO 2 52 .78 55 .40 tr. 55 47 
MgO .07 35 tr. -07 22 79 54 13 
CaO 45 P .22 28 1.20 95 1.05 I.10 
Na,O 4.51 5.30 6.51 5.45 6.62 Fol 7-3 OMe ONiZ 
K,0 3-96 4.090 3.22 5.29 4.98 5.25 5.50 5.43 
H,O 25 tr. 0.33 05 .50 -70 1.90 1.77 
99-38 99.89 100.89 100.62 99.60 100.10 100.33 99.83 
. Grorudite, Varingskollen, Norway. 
. Grorudite, Grorud, “ 
. Grorudite, Kallerud, as 
. Grorudite, Fron, Ny 
. Quartz-bearing Solvsbergite, “‘ 
. Nearly quartz-free Solvsbergite, Lougenthal, Norway. 
Nephelin-bearing Solvsbergite, Tjose-Aklungen, Norway. 
. Tinguaite, Hedrum, Norway. 
oN AM FW WN 
tematic classification of igneous rocks in various directions. 
This may be shown graphically as inthe accompanying diagram, 
where the series of analyses are plotted so as to bring out the 
relation between the total alkalies and the silica in each case. 
The grounds for this method of comparison will not be gone 
into at this time, owing to lack of space, only the results can be 
given. The molecular proportion between the sum of the 
alkalies and silica in each case is expressed in parts of a hundred, 
which are used as ordinates. The silica percentages are used 
as abscissas, the highest being placed at the left. Hence the 
most silicious rocks are at the left hand end of the diagram, 
and those with the smallest ratio of alkalies to silica at the bot- 
tom. The rocks with least alkalies are at the lower right hand 
corner of the diagram. The location of the various rocks in 
such a scheme is indicated by different symbols. 
