282 
ELEMENTS OF GEOLOGY. 
which have the same kind of interest to a geologist which 
certain mediaeval records excite when we study the history 
of nations. For both of them throw light on ages of dark¬ 
ness, preceded and followed by others of which the annals 
are comparatively well known to us. But these newly-dis¬ 
covered records do not fill up the wide gap, some of them 
being closely allied to the Eocene, and others to the Creta¬ 
ceous type, while none appear as yet to possess so distinct 
and characteristic a fauna as may entitle them to hold an 
independent place in the great chronological series. 
Among the formations alluded to, the Thanet Sands of 
Prestwich have been sufficiently described in the last chap¬ 
ter, and classed as Lower Eocene. To the same tertiary 
series belong the Belgian formations, called by Professor 
Dumont, Landenian. On the other hand, the Maestricht 
and Faxoe limestones are very closely connected with the 
chalk, to Avhich also the Pisolitic limestone of France is refer¬ 
able. 
Classification of the Cretaceous Eocks. — The cretaceous 
group has generally been divided into an Upper and a Low¬ 
er series, the UjDper called familiarly the chalky and the Low¬ 
er the greensand; the one deriving its name from the pre¬ 
dominance of white earthy limestone and marl, of which it 
consists in a great part of France and England, the other or 
lower series from the plentiful mixture of green or chloritic 
grains contained in some of the sands and cherts of which it 
largely consists in the same countries. But these mineral 
characters often fail, even when we attempt to follow out 
the same continuous subdivisions throughout a small portion 
of the north of Europe, and are worse than valueless when 
we desire to apply them to more distant regions. It is only 
by aid of the organic remains which characterize the suc¬ 
cessive marine subdivisions of the formation that we are able 
to recognize in remote countries, such as the south of Europe 
or Uorth America, the formations which were there contem¬ 
poraneously in progress. To the English student of geology 
it will be sufficient to begin by enumerating those groups 
which characterize the series in this country and others im¬ 
mediately contiguous, alluding but slightly to those of more 
distant regions. In the annexed table it will be seen that I 
have used the term ISTeocomian for that commonly called 
“ Lower Greensandas this latter term is peculiarly objec¬ 
tionable, since the green grains are an exception to the rule 
in many of the members of this group even in districts where 
it was first studied and named. 
