A N:o 1) Igneous Rocks of Sviatoy Noss in Transbaikalia. 33 
highly siliceous rocks, but in this case the FeO: MgO ratio is 
higher in the basic dike-rock than in its granodioritic country- 
rock, from whose magma it has obviously been derived. 
It was suggested from the field observation concerning 
this and other similar dikes that the aplite and the kersantite 
should represent a diaschistic suite. We may therefore com- 
pare the analyses of both dike-rocks with that of the surround- 
ing granodiorite. 
I is the analysis of the aplite, II that of the kersantite 
and III that of the granodiorite, all from Mys KR 
IV is the average of 5 parts of I and 3 parts of II. 
IE II. III. IV. 
Sl035 738015, 103 05,065 05.32 
KSO ESS OLSEN dOBÅ LG 
KesOs- 057 2.02 1.74 1.11 
FeO 1.22 7.48 2.51 3.57 
 MnO = 0.05 0.21 0.08 0.11 
MORA ST 1.31 0.92 
CaO 1.18 7.29 3.28 3.47 
Na0 = 3.14 4.24 4.16 3.55 
KROAT 0:20 2.80 4.82 4.96 
TiO. 20:33 1.20 0.63 0.66 
12 AR NS AS ANN Os 0.26 0.36 
30: 0:33 0.42 0.57 0.36 
100.387 99.37 —100.26 100.24 
The ratio 5: 3 was chosen, because a simple calculation 
showed the aplite and kersantite, if mixed in this proportion, 
to give approximately the same percentage of silica as that 
of the granodiorite. It is now quite astonishing to find a 
very close agreement in all the other oxides also. Greatest 
disagreement is found in the iron oxides, but the deviation 
in the ferric oxide is opposite to that in the ferrous oxide. 
The diaschistic nature of these and other dike series 
thus seems obvious. But the relations must not be under- 
stood as if the average composition of all the existing dikes 
should be identical with that of the granodiorite-granite- 
; 3 
