Re: Four Rivers Revisited

Allen Roy (
Sun, 2 May 1999 17:54:01 -0700

Jonathan wrote:
> Portland cement is composed of aluminosilicates formed from a mixture of
> iron oxides, bauxite, and limestone calcined at about 1500 degrees C.
> result is a mixture of mainly dicalcium and tricalcium silicates with
> amounts of tricalcium aluminate and tetracalcium aluminoferrite. Gypsum
> (hydrated calcium sulphate) is then added.

I worked for several years as a Civil Engineering Tech inspecting the
construction of Interstate roadways and concrete bridges. I learned a
little something about cement and concrete. :)

> Primary cements in carbonate sediments include high and low magnesium
> and aragonite. These typically are stablised as calcite and are
> partly to wholly replaced by dolomite or quartz. Sandstones may be
cemented by
> carbonates, quartz, feldspars, clays or micas. All cements are
> from saturated solutions that percolate through the sediment.

In a catastrophic setting, the sandstones would be deposited from carbonate
or silicate rich waters. The deposit would become cemented by precipitated
minerals from the water solution which saturates the sands. One need not
wait for reletively slow percolation to do the job.

> Portland cement has absolutely no counterpart in the non-human world.
> composition and the processes by which it is manufactured and forms
> bears no relationship to sedimentary cements and cementation whatsoever.

The ancient Romans made concrete, while not as good as our Portland cement,
from simpler recepies consisting primarily of lime. Deposits of lime mud
would not take too long to harden.