| _Craie glauconieuse_| | |
+-----------------------------------------------+---------------------+----------+-----------+
* (See table in article CRETACEOUS SYSTEM,)

Since Prof. Barrois introduced the zonal system of subdivision (C. Evans
had used a similar scheme six years earlier), our knowledge of the
English chalk has been greatly increased by the work of Jukes-Browne and
William Hill, and particularly by the laborious studies of Dr A.W. Rowe.
Instead of employing the mixed assemblage of animals indicated as zone
fossils in the table, A. de Grossouvre proposed a scheme for the north
of France based upon ammonite faunas alone, which he contended would be
of more general applicability (_Recherches sur la Craie Superieure_,
Paris, 1901).

The Upper Chalk has a maximum thickness in England of about 1000 ft.,
but post-cretaceous erosion has removed much of it in many districts. It
is more constant in character, and more typically chalky than the lower
stages; flints are abundant, and harder nodular beds are limited to the
lower portions, where some of the compact limestones are known as "chalk
rock." The thickness of the Middle Chalk varies from about 100 to 240
ft.; flints become scarcer in descending from the upper to the lower
portions. The whole is more compact than the upper stage, and nodular
layers are more frequent--the "chalk rock" of Dorset and the Isle of
Wight belong to this stage. At the base is the hard "Melbourne rock."
The thickness of the Lower Chalk in England varies from 60 to 240 ft.
This stage includes part of the "white chalk without flints," the "chalk
marl," and the "grey chalk." The Totternhoe stone is a hard freestone
found locally in this stage. The basement bed in Norfolk is a pure
limestone, but very frequently it is marly with grains of sand and
glauconite, and often contains phosphatic nodules; this facies is
equivalent to the "Cambridge Greensand" of some districts and the
"chloritic marl" of others. In Devonshire the Lower Chalk has become
thin sandy calcareous series.

The chalk can be traced in England from Flamborough Head in Yorkshire,
in a south-westerly direction, to the coast of Dorset; and it not only
underlies the whole of the S.E. corner, where it is often obscured by
Tertiary deposits, but it can be followed across the Channel into
northern France. Rocks of the same age as the chalk are widespread (see
CRETACEOUS SYSTEM); but the