Claypole on Darwin and Geology. 211 
the minerals enumerated in this part of the dyke, there is in 
prominent porphyritic development an altered rhombic pyrox- 
ene. The alteration has proceeded very far and the mineral is 
now represented only by a mass of yellowish green serpentine 
with perhaps some of the intermediate alteration product bastite. 
The cleavage is, however, well defined and the extinction in the 
several cases noted is sharply parallel to it. These characters 
together with the traces of the obtuse dome so characteristic of 
sections of enstatite are sufficient to identify it as that mineral 
in an altered state. The occurrence of the enstatite in this dyke 
in its finer gi'ained parts towards the contact is analogous to, and 
an interesting confirmation of the similar occurrence of the min- 
eral noted in the Jack Fish lake dyke also in the vicinity of its 
contact. 
To summarize, the main points of interest are, briefly: i. 
Post Archtean age of dykes. 2. Their problematic relation- 
ship to traps of the Animikie and Keeweenawan. 3. Their uni- 
form strike and width. 4. Sharp contact. 5. Passage from 
coarse texture at centre to aphanitic at sides. 6. Granular 
character towards centre, porphyritic at sides. 7. Prevalence 
of quartz and garnets towards centre, and absence near con- 
tact. 8. Presence of enstatite at sides, absence towards centre. 
9. " Chloritic substance" abundant at sides, absent towards 
centre. 10. Polysomatic character of augite throughout. 11. 
Uralitization of augite. 12. Very marked contrast of texture of 
two different parts of a rock mass which solidified under jjractic- 
ally the same prcss/irc but at different rates of cooling. 
YProc. Can. Inst. T'oro7tto^iS8'j.~\ 
DARWIN AND GEOLOGY. 
BY PKOF. E. W. CLAYPOLE. 
{Continued from p. i62?^,^''^ *0 ^ 
In the comparative seclusion afforded by his five years on the 
"Beagle"^ the mind of Darwin gradually drifted toward the 
' In connection with tlie immense amount of -work performed in later 
years we may note that his Iicalth was never good after this voyage. 
The cause does not seem to have been evident. Speaking of a little tour 
