Having treated in the preceding chapters of the tertiary strata, we have next to speak of the uppermost of the secondary groups, called the Chalk or Cretaceous (No. 6. Table, p. 103.), because in those parts of Europe where it was first studied its upper members are formed of that remarkable white earthy limestone, termed chalk (_creta_). The inferior division consists, for the most part, of clays and sands, called Greensand, because some of the sands derive a bright green colour from intermixed grains of chloritic matter. The cretaceous strata in the north-west of Europe may be thus divided[209-A]: _Upper Cretaceous._ 1. Maestricht beds and Faxoe limestone. 2. Upper white chalk, with flints. 3. Lower white chalk, without flints, passing downwards into chalk marl, which is slightly argillaceous. 4. Upper greensand. 5. Gault. _Lower Cretaceous._ 6. Lower greensand--Ironsand, clay, and occasional beds of limestone (Kentish rag). _Maestricht Beds._--On the banks of the Meuse, at Maestricht, reposing on ordinary white chalk with flints, we find an upper calcareous formation about 100 feet thick, the fossils of which are, on the whole, very peculiar, and all distinct from tertiary species. Some few are of species common to the inferior white chalk, among which may be mentioned _Belemnites mucronatus_ (see fig. 197.) and _Pecten quadricostatus_. Besides the Belemnite there are other _genera_, such as Ammonite, Baculite, and Hamite, never found in strata newer than the cretaceous, but frequently met with in these Maestricht beds. On the other hand, Volutes and other genera of univalve shells, usually met with only in tertiary strata, occur. The upper part of the rock, about 20 feet thick, as seen in St. Peter's Mount, in the suburbs of Maestricht, abounds in corals, often detachable from the matrix; and these beds are succeeded by a soft yellowish limestone 50 feet thick, extensively quarried from time immemorial for building. The stone below is whiter, and contains occasional nodules of grey chert or chalcedony.