THE NATUBAL SCIENCE JOUBNAL. 
43 
best attempts are easily detected even by 
a novice. 
While some Mexican mines produce 
valuable gems, others near by yield 
stones fine to look upon at first, but 
which in a few days begin to grow cloudy 
and crack, and in a month fall into value¬ 
less fragments; yet even these if put 
into water or oil will remain intact indefi¬ 
nitely. 
Other stones which do not fracture, 
change from transparent to opaque white¬ 
ness, assuming more beautiful fire in 
such transition. 
Some very misleading statements have 
been written concerning the mines near 
Queretaro. It is many years since the 
Jurado mine has been worked. It caved 
in one day or night and the owners and 
miners have been so busy wrestling with 
their great inactivity, that it remains in 
that state to this day. 
The Esperanza is worked now and 
again in a manner that would ruin any 
mine; and what I say of it would apply 
equally to other mines. I do not think 
of a single exception. The owners of 
the mines are wealthy, and do not .work 
them because they do not care to. If 
you ask them “Why not?” they will 
tell you, “ We do not have to.” 
Now to explain how the mines are 
worked. 
The owner rents the mine or a certain 
part of it to two men or more—they 
always work in pairs—at from $1.00 to 
$3.00 per week, or more should the 
mine be in a promising condition. These 
men get out of it what they can by 
gouging, and in a short time leave it in 
the poorest sort of condition. The next 
set of men must do “ dead work,” which 
is work without hope of remuneration, in 
order to get the mine in shape for work¬ 
ing. These in turn leave it in worse 
shape than the others, if this be possible. 
So the gouging goes on. The Esperanza 
produces gems of which many contain 
“ straws ” — imperfections resembling 
straws. The Sierra Grande yields stones 
that are fine when taken out, but they 
crack and crumble. For this reason it 
is not worked. 
Of course it is understood that all 
mining work is done by blasting, and on 
coming from the mine opals have the ap¬ 
pearance of pebbles in pudding stone. 
The matrix being jasper and the opal the 
more brittle of the two, many more are 
lost than saved by breaking them out 
with hammer and chisel. Broken in 
pieces varying in size from a tiny frag¬ 
ment to a cobblestone, they are sold to 
the lapidary. 
(to be continued.) 
The Chinese wall is the most exten¬ 
sive fortification in the world. Accord¬ 
ing to the surveys made within the last 
few years, this wall is 1,728 miles in 
length, reaching from the gulf of Pechee- 
lee to some distance past Soo-Choo, on 
the confines of Turkestan. This remark¬ 
able structure passes up steep mountains, 
down into gorges and ravines, crosses 
rivers, valleys and plains, seemingly re¬ 
gardless of obstacles. It is 25 feet thick 
at the bottom and 15 feet at the top, and 
25 to 30 feet in height, with flanking 
turrets or towers 35 to 40 feet high, 
every 200 or 300 yards of its length. Its 
erection was begun in 211 B. C., and it 
was designed to protect the northern 
frontier of China against the savage 
tribes of Siberia. 
