282 
Minerals. Time exposed. Weightingrms, Weightingrms, Lossin 
before. after. weight. 
Corundum Crystal, 30 seconds, 1:49 0:22021 1:16979 
Emery, Chester, Mass., 1 minute, 16°65 11-6968 4:9532 
Topaz (goute d’eau), 1 minute, 2-097 071263 1:9707 
Topaz pebble, 1 minute, 9°74 76241 2°1499 
Black Diamond, 3 minutes, 1:2607 1:2235 0°0372 
sa e elias 1°2235 1:1738 00497 
et of ore 1:2607 11738 0-0869 
In a former experiment, a hole nearly 2 of an inch above, 
and } an inch below, was bored through a corundum crystal 
from Ceylon, one half an inch thick, in 8 minutes. The 
weight of this crystal previous to the operation was not 
taken, but the crystal is preserved in the mineral collec- 
tion of the School of Mines. In the Emery from Chester, 
a large hole was made, in which pieces of corundum project, 
showing that the blast acted much faster on the magnetite 
than on the corundum. A conical hole was made in the 
Topaz pebble, the point of the cone being quite sharp. The 
microscopic examination of these specimens, showed that 
they all presented the same general appearance. The Emery 
was worn away in a manner very similar to that which is so 
often seen on the surfaces of rocks near sand beaches, which 
are exposed to violent winds carrying sand with them, and 
suggested to me, whether more importance should not be 
given to this agent as a power of degradation, and as the 
cause of many phenomena in structural geology not hitherto 
explained. If such effects can be produced by the fan 
blast in a very short time, is it not likely that the action of 
the wind at ordinary velocities continued a very long time, 
will produce much more powerful effects on a large scale, and 
may we not expect that a hurricane would produce effects 
similar to that produced by the injector machine with 
steam. The peculiar chatoyant lustre of many minerals I 
was able to produce at will, on any mineral possessing 
cleavage, by a few moments’ exposure to the blast. It 
seems probable that many of the rounded faces of minerals 
which have this lustre may have been produced in this way, 
and that many of those rounded surfaces noticed on minerals 
which have no cleavage may be traced to this cause. It 
