, 1912-03-02

More than that, this grand sheet stretches
far away where it can no longer be seen
from England, for it hnderlies Denmark.
seldom showing itself, but generally COW
cred by newer formations, in some cases
so little covered, however, that it can easily
be got at, and used, aud it is used on q
great scale in the very industry that we are
speaking of, for chalk plays a very large part
in the recent history of cement marufncture.
The chalk formation is known, from the
shells and other Animal remains found in it.
to have been deposited on the bed Of the
ocean, it is in. fact mainly composed Of
myriads of inmate shells and fragments Of
such. The London clay, on the other hand
has been deposited partly in the estuary Of
arlurge river, rs we know from the numbers,
Of leaves and frdits oEtained from soi:e Of
its cliffs at the same. time much of The mud
MIDST have been carried out to sea, Tor parts"
OF, the formation contain" many sea-shefls. az
We may now go back to the blocks Of
stone which we're ished up from the sea-
bottom off Harwich aud converted into'cg-
ment. layers of such books are common
in some parts Of the London clay. The
history of their formation is curious. The
clay at the various levels where the books
have b2en formed hCs evidently contained
more lime than usual, and this III q state. OF
solution his tended to draw together, form
ing what are called corrections. Thin ho-
rizontal bands of clay are often seen pass
ing through the Blocks, proving their
origin. The outer part of each block has,
evidently hardened first, after which the i1r
terror has continued TO dry, which has cersed
the mass to shrink and to develope numerous
cracks from the centre outWArds. This PEI
culiarity has gained for these concretions
the name of .Sep&0rj0, the word implying
Shat the stone rs partitioned. The CRACKS
have been subsequently filed IN with carbo-
nate of lime, and the block has ultimately come
to contain much more lime than clay. 1t
was the natural mixture of lime and clay
that made the stones valuable at that timer
for it was known that on being burned they
would make q mortar which would harden
under water and for that reason is called Ayr
draulic cement. That they we've got from of
shore is easily explained. In q by-gone aga
the clay beds had extended much farther
out, but the sea has since deVoured the land,
leaving the stones scattered about the bottom
Perhaps tire Harwich industry no, longer
exists, the Roman, cement l1fts, probably been
displaced by the Portland, in which Natures
mixture Of lime aud cay has been artlhcaliy
initiated.
It was many years after leaving Harwich
that the writer, while V sitting the old city or
Rochester on the so It'll bank of the Midway,
q small river Wncn JOINS Gne LuaLneS ehCN"lIH
saw a number of factories on the north side of
the river and was told that they We're Po1t-
land cement factories and that the cement was
made by mixing chalk with the mud of the
river.
Professor Ansted, in his"Geology," explains
the name Portland as being given to the ce-
nlent "frorG the slight resemblance IN colour
shown by this cement to the stone so called
Slight indeedi it is, for the writer, when visit
ing Portland at the time OF the constructions
OF the fine b~reakwater there, saw great guam
titles of the stone, and remembers it as beng
of q fine cream colour: The r. ofessor gives
the following account Of the mapufacttHEe.9
"Portland cement is made from. carbonate
of lime, (chalk in this CASEY mixed With great
care, in definite proportions, with lhe muddy
deposits Of rivers running over clay and
chalk. The whole of the materials are care
fully pounded together under waters anG are
afterwards dried and burned"
There can be no doubt that this kind OF
cement is rapidly becoming of more and more
Importance in the world. Perhaps the day IS
approaching when Mr.. Edison's plan for
erOurino" houses instead of building them