CKETACEOUS PERIOD. 
281 
SECONDAEY OR MESOZOIC SERIES. 
CHAPTER XVII. 
UPPER CRETACEOUS GROUP. 
Lapse of Time between Cretaceous and Eocene Periods.—Table of succes¬ 
sive Cretaceous Formations.—Maestricbt Beds.—Pisolitic Limestone of 
France.—Chalk of Faxoe.—Geographical Extent and Origin of the White 
Chalk.—Chalky Matter now forming in the Bed of the Atlantic.—Marked 
Difference between the Cretaceous and existing Fauna.—Chalk-flints.— 
Pot-stones of Horstead.—Vitreous Sponges in the Chalk.—Isolated Blocks 
of Foreign Rocks in the White Chalk supposed to be ice-borne.—Distinct¬ 
ness of Mineral Character in contemporaneous Rocks of the Cretaceous 
Epoch.—Fossils of the White Chalk.—Lower White Chalk without Flints. 
—Chalk Marl and its Fossils.—Chloride Series or Upper Greensand.— 
Coprolite Bed near Cambridge.—Fossils of the Chloride Series.—Gault.— 
Connection between Upper and Lower Cretaceous Strata.—Blackdown 
Beds.—Flora of the Upper Cretaceous Period.—Hij)purite Limestone.— 
Cretaceous Rocks in the United States. 
We have treated in the preceding chapters of the Tertiary 
or Cainozoic strata, and have next to speak of the Second¬ 
ary or Mesozoic formations. The uppermost of these last is 
commonly called the chalk or the cretaceous formation, from 
creta^ the Latin name for that remarkable white earthy lime¬ 
stone, which constitutes an upper member of the group in 
those parts of Europe where it was first studied. The mark¬ 
ed discordance in the fossils of the tertiary, as compared 
with the cretaceous formations, has long induced many ge¬ 
ologists to suspect that an indefinite series of ages elapsed 
between the respective periods of their origin. Measured, 
indeed, by such a standard, that is to say, by the amount of 
change in the Fauna and Flora of the earth effected in the 
interval, the time between the Cretaceous and Eocene may 
have been as great as that between the Eocene and Recent 
periods, to the history of which the last seven chapters have 
been devoted. Several deposits have been met with here 
and there, in the course of the last half century, of an age in¬ 
termediate between the Avhite chalk and the plastic clays 
and sands of the Paris and London districts, monuments 
