214 M. Alex. Brongniart sur les caracteres Zoologiques, &c. 
formations which M. B. refers to chalk, are found in very 
distant localities and with very different characters of con-_ 
sistence, stratification, colour, super-position, &ec.; ye 
from similarity or identity of the fiosils imbedded in them, 
he refers them all to the general head of the Chalk 
Formation. He divides this formation into 3 sub-forma- 
pare superior or White Chalk—the middle or Chalk 
Tufa—and the inferior or Green-sand, (Glauconie tn 
Br.), i.e. chalk mixed with green grains ascertained by 
M. Berthier, to be silicated hydrate of iron, and not chlo- 
rite, as had been s supposed. These 3 sub- formations inclose 
fossil —_ which are in part dif in each, and in 
com = 
cr first. cauadem the value f Zoological characters 1% 
. The species of abellae? zoophy tes, ae eres in forma- 
tions of different periods fer from e : 
ihe formations, as in pitdeton te:thes ieee ular dis- 
tance. This law nov well established, and its apparent 
exceptions have been in most cases accounted for by the 
particular circumstances attending them, and have thus 
been reduced to the general rule. It follows from this 
that the different formations, which overlie each other on 
the more ir a were formed at different and distant 
achat chemical Compositions, structure in mass, 
superposition, accompanying minerals, &c. ; but some- 
times these differences are in apparent opposition to the 
ils.— 
gota differences derived Pas imbedded fossi 
on to be answered then, is the following : 
& ein in two dimacie formations, the rocks are differe 
in mineralogical characters, whilst their organic ‘remains 
are analogous, ought we to regard them as of distinet for- 
or, On account of the general well a re- 
semblance of the fossils imbedded, to consider the 
same period of formation, when the order of ccbenpasiirn 
cod 
= 
