sses up into a great
mass of white chalk, in which the stratification is marked by
nodules of black flint arranged in layers (_Senonien_ of D'Orbigny;
_Oberquader_ of Germany). The thickness of these three subdivisions
taken together is sometimes over 1000 feet, and their geographical
extent is very great. White Chalk, with its characteristic
appearance, may be traced from the north of Ireland to the Crimea,
a distance of about 1140 geographical miles; and, in an opposite
direction, from the south of Sweden to Bordeaux, a distance of
about 840 geographical miles.

VI. In Britain there occur no beds containing Chalk fossils, or
in any way referable to the Cretaceous period, above the true
White Chalk with flints. On the banks of the Maes, however, near
Maestricht in Holland, there occurs a series of yellowish limestones,
of about 100 feet in thickness, and undoubtedly superior to the White
Chalk. These _Maestricht beds_ (_Danien_ of D'Orbigny) contain a
remarkable series of fossils, the characters of which are partly
Cretaceous and partly Tertiary. Thus, with the characteristic
Chalk fossils, _Belemnites, Baculites_, Sea-Urchins, &c., are
numerous Univalve Molluscs, such as Cowries and Volutes, which
are otherwise exclusively Tertiary or Recent.

Holding a similar position to the Maestricht beds, and showing
a similar intermixture of Cretaceous forms with later types, are
certain beds which occur in the island of Seeland, in Denmark,
and which are known as the _Faxoee Limestone_.

Of a somewhat later date than the Maestricht beds is the _Pisolitic
Limestone_ of France, which rests unconformably on the White
Chalk, and contains a large number of Tertiary fossils along with
some characteristic Cretaceous types.

The subjoined sketch-section exhibits the general succession of
the Cretaceous deposits in Britain:--

[Illustration: Fig. 185. GENERALIZED SECTION OF THE CRETACEOUS
SERIES OF BRITAIN.]

In North America, strata of Lower Cretaceous age are well represented
in Missouri, Wyoming, Utah, and in some other areas; but the greater
portion of the American deposits of this period are referable to
the Upper Cretaceous. The rocks of this series are mostly sands,
clays, and limestones--_Chalk_ itself being unknown except in
Western Arkansas. Amongst the sandy accumulations, one of the
most important is the so-called "marl" of New Jersey, which is
truly a "Greensand," and contains a large proportion of glauconite
(sil