462 Scientific Intelligence. 
vades the whole rock, as ae perlites. (2) Cooking —— pron 
fragments taken up in a lava flow; this see erely a 
marginal structure connected with the igeeits ad. fea "affect. 
ing the rest of the rock. (3) By the tension in the surrounding 
mass when a crystal is formed ; Ay formation of a crystal not 
rhe involving perlitic fissior 
author gives an interesting isu of the development of 
ictinta in glass along fissures. He says: “ Fifteen or twenty 
years ago a house was burnt down in the market-place m5 Dover; 
a small piece of plate-glass from one of the windows is seen, 
when closely examined, to be traversed by minute, irregular 
cracks like those in the artificially cracked, carmine-staine quartz 
of the French jewelers, known as trubace. "When ex taniied under 
is 
spherules with ig Meine? beeen structure, each traversed by 
the usual dark cross. That they follow the cracks is evident, 
the upper surface of the glass downward. They a 
really iicwttat erystalline films like little flat wheels lying on the 
cracked surfaces of the glass. The phenomenon is superficial 
and seems only to follow the cracks e may feel tolerably sure 
that the glass was not cracked in this manner before the house 
was burnt. The cracks are precisely such as would be produced 
in glass or rock crystal by heat and subsequent immersion in @ 
cold solution; and these conditions would, in this case, be fulfilled 
by the fire and the pla ay of water from the fire-engines. Whether 
those little circular Shar ps ese es gr represent crystallization 
set up actually iz the glass, or result from the erystallization of 
some substance other than that of the ‘ilies, introduced in solu- 
~ tion into the fissures, I am not prepared to say.” 
II. GroLtogy AND MINERALOGY. 
a 
Duluth and from Duluth to Nipigon Bay. The rocks of the 
Animikie group, about Thunder Bay, are excluded, and referred 
to the Huronian age; and also the horizontal Lake uperior 
h. 
a coast region eastward, are made to be unconformable and 
