This historic book may have numerous typos and missing text.
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(without typos) from the publisher. Not indexed. Not illustrated.
1918 Excerpt: ...of foraminifera, showing in many cases the
delicate details of the external form of the shells. In some
instances the lime carbonate of the shells is still present, not
having been leached out. Under the microscope these white shales
are found to consist largely of opaline silica in which there are
very small amounts of argillaceous matter together with a few
minute, angular grains of quartz, and an occasional grain of
feldspar. These mineral grains may make up as much as five per cent
of the volume of the rock. "When the lime carbonate of the
foraminiferal shells is still present it is seen to be in the form
of fibrous aragonite. The minute perforations of the shell appear
clearly in such instances, and the chambers are usually filled with
crystalline calcite. In most of these white opaline shales there
are no other organic remains. By treating the diatomaceous shales
and the white opaline shales with caustic potash, amorphous silica
gocs into solution to an amount from fifty to seventy per cent.
After dissolving the opaline or amorphous silica the residue
consists of minute grains of quartz, feldspar and various other
minerals, together with some argillaceous material. In addition to
these substances there are often numerous fragments of volcanic
glass. In some cases a large proportion of the rocks consist of
this material so that gradations exist between the typical shales
and acid tuffs. MONTEREY CHERTS In addition to the shales,
siliceous rocks of a cherty nature are found in the Monterey
generally at definite horizons. The cherts of the Monterey group
may be divided into two types: the bedded cherts and the flinty
cherts. The bedded cherts are like the cherts of the Franciscan in
that they are rhythmically interbedded with shales. The flinty
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||Paperback - Trade
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