36 Canadian Record of Science. 
transparent slides interveining to separate the two. In 
reflected light, too, pyrite is seen to be a not infrequent 
constituent. 
In another section the original shape of the grains is out 
lined by iron hydroxide, and they have a peculiar frayed 
out edge, the brown material also forming a faint demar- 
cation of the outlines of the large quartz crystals composing 
the interstitial mosaic. 
Whilst the grains are generally rounded, there is a cer- 
tain proportion of sub-angular fragments, but these would 
seem to result from the disintegration of the original rounded 
particles during the process of decomposition and solution, 
and often where the grain retains its primary shape numer- 
ous fissures are seen to penetrate towards its centre, which 
are filled with crystallized quartz similar to that surround- 
ing it and present an incipient stage of the breaking-up 
process. 
The mergence from the distinctly grained varietics into 
the compact cherts will be frequently illustrated in the 
same hard specimen, and examination of a thin section 
from such a one clearly shews the nature of the process to 
which the effect is due. Viewed in ordinary light, a por- 
tion of such a slide will shew distinctly marked grains with 
transparent quartz surrounding them. Passing towards the 
other edge of the section, representing the compact cherty 
part of the original specimens, the grains are found to shew 
less and less distinctly, until a portion is reached consisting 
apparently of nothing but transparent quartz, somewhat 
clouded in places, and with a few distributed areas of mag- 
netite and iron hydroxide. An examination under polar. 
ized light, however, brings out the original structure by 
the contrast between the fine crystallization of the quartz 
replacing the original graiv and that interstitially deposited. 
Occasionally specimens of a pretty wavily marked variety 
of the cherts will be found. A section of such a one shows 
it to be similar in nature to the rest, except for the general 
parallel appearance produced by the drawing out of its 
constituents, The mass of the section is made up of a 
Tae 
