Petrographical Differentiation of certain dykes. 161 
notes as the White-fish Bay dyke, was analyzed with the following 
results : 
White-fish Bay dyke. 
I 
II 
III 
IV 
Si0 2 
47.50 
•48.08 
52.47 
Fe 2 O s +FeO 
7.40 
9.07 
6.31 
A1 2 3 
22.44 
23.67 
25.54 
CaO 
10.21 
10.99 
6.62 
Ms? 
3.71 
3.92 
2.31 
K 2 
1.29 
.49 
.54 
Na 2 
f.62 
1.92 
3.23 
p 2 o 5 
• .34 
1.11 
L.16 
Loss on ig 
2.85 
.83 
1.2S 
97.36 
3.081 
100.08 
99.46 
Sp. g. 
2.927 
3.030 
■ 
2.870 
I near contact with dyke wall. 
II six feet from contact. 
III thirty feet from contact. 
IV sixt} T feet from contact (middle of dyke). 
In this dyke the gradation in texture is as pronounced as in the 
Stop Island dyke hut the differentiation of structure is not so 
marked. In I the ground mass has the character of a fine-grained 
ophitic diabase and the porphyritic constituents present no great 
contrast in size to those of later generation which have crys- 
tallized around them ; and iii IV the ophitic structure is not en- 
tirely replaced by the granular. This dyke is noteworthy for the 
abundance of hypersthene which is present near the dyke walls. 
This hypersthene is a porphyritic constituent, and has well defined 
crystallographic form. It has not been observed in specimens 
from other portions of the dyke and its occurrence recalls the 
similar occurrence of enstatite in the Jack-fish Lake dyke and in 
the Rat-root Bay d3'ke which has been noted in a former paper. 
There is as in the Stop Island dyke a regular increase in the pro- 
portion of quartz in passing from the dyke walls to the middle 
and in the latter part of the dyke the augite is entirely replaced 
by hornblende. The analyses of this dyke rock and of the Stop 
Island dyke rock show throughout an unusually high percentage 
of alumina. 
A dyke sixty-five feet wide cutting biotite gneiss with a 
northwest strike on the north shore of Shoe Bay. Rainy Lake, 
13 
