298 
ELEMENTS OF GEOLOGY. 
Fig. 262. land to be the excrement of fish (see 
Fig. 262). They are composed in great 
part of phosphate of lime. 
Lower White Chalk. — The Lower 
White Chalk, which is several hundred 
feet thick, without flints, has yielded 25 
species of Ammonites, of which half are 
peculiar to it. The genera Baculite, 
Hamite, Scaphite, Turrilite, I^autilus, 
Coprohtes of fish, from the Belemnite, and Belemnitella, are also 
represented. 
Chalk Marl. —The lower chalk without flints passes grad¬ 
ually downward, in the south of England, into an argilla- 
Fig. 263. 
Baculites anceps, Lam. Lower chalk. 
eeous limestone, “ the chalk marl,” already alluded to (p. 
286). It contains 32 species of Ammonites, seven of which 
are peculiar to it, while eleven pass up into the overlying 
lower white chalk. A, 
Hhotomagensis is charac¬ 
teristic of this formation. 
Among the British cephal- 
opods of other genera may 
be mentioned Scaphites 
265). 
Chloritic Series (or Upper 
Greensand). — According 
to the old nomenclature, 
this subdivision of the 
chalk was called Upper 
Greensand, in order to distinguish it from those members of 
the Neocomian or Lower Cretaceous series below the Gault 
to which the name of Greensand had been applied. Besides 
the reasons before given (p. 282) for abandoning this nomen¬ 
clature, it is objectionable in this instance as leading the un¬ 
initiated to suppose that the divisions thus named Upper 
and Lower Greensand are of co-ordinate value, instead of 
which the chloritic sand is quite a subordinate member of 
the Upper Cretaceous group, and the term Greensand has 
very commonly been used for the whole of the Lower Creta¬ 
ceous rocks, which are almost comparable in importance to 
mqualis (Fig. 266) and 
Turrilites costatus 
Fig. 264. 
Ammonites Rhotomagensis. Chalk marl. 
Back and side view. 
