450 Dr. A. Holmes and Dr. S. Smith— 
These results reveal a remarkable similarity between the rocks 
investigated, and even though they cannot be considered as strictly 
accurate, they suggest in a general way a correlative feature to which 
attention was first directed in a recent paper by one of us (A.H.) on 
“The Basaltic Rocks of the Arctic Region ’’.! It was there shown 
that in the over-saturated basalts of Iceland and the Faroes the black 
ores decreased as the felspars increased, and the same kind of | 
relation, though with a different correlative factor, was found to hold 
among the olivine-basalts of Iceland. As soon as chemical analyses 
became available, it was found that the antipathy could be best 
expressed by comparing titanium dioxide with normative plagioclase, 
and that a simple relation existed between these constituents 
which held for nearly all the analysed olivine-free basaltic rocks 
from Siberia in the north-east to Greenland on the north-west and 
Mull in the south. The exceptions were found to be somewhat 
abnormal in texture and composition, as they all contained numerous 
glomero-porphyritic aggregates of bytownite. 
A suggestion of a similar antipathetic relation between felspars 
and ores is detectable in the results here presented, as shown by the 
weight-percentages :— 
Felspars . 43°4 AT-4 49:0 48:7 
* Black Ores . 113 10°8 10-1 9°3 
Tested by the available analyses, which unfortunately are few at 
present, and in the case of the Hett dyke, too poor to be of service, 
the significant antipathetic variation of titanium dioxide and 
normative plagioclase is found to hold. And not only so, but the 
correlative factor approximates so closely to that of the Brito- 
Arctic unsaturated basaltic rocks that the figures fit into the series 
with only a very slight discrepancy. 
Titanium Normative 
Locality. Dioxide.  Plagioclase. 
Spitzbergen ; ; 2:93 42-56 
Mull . 6 : 2°80 42°49 
Whin Sill (B) : : 2°42 44°83 
Franz Josef Land : 2°29 46°63 
Wackerfield (A) . é 2°22 45°36 
Whin Sil (C) .. : 1°92 47°21 
Kuzkin Island . ; 1°63 51°30 
Mull . ! ; ; 1:46 59°36 
Mull . : 5 i 1:46 61°83 
Mull . 2 0:93 66:16 
We hope in a later paper to pee analyses by means of which the 
suggested relation may be tested more rigorously. There can be 
no doubt that the Brito-Arctic Tertiary rocks are derivates from a 
regional magma or series of magmas of uniform composition, in which 
some continuous process of differentiation has brought about the 
remarkable relation which has been disclosed. It seems probable 
that by the sinking of olivine crystals a separation of under- 
1 Min. May., vol. xviii, 1918, p. 216. 
